Where Can I See Meteorite Impact Craters in the United States?

American Impact Craters

The face of the Moon is a quiet testament to a violent past. Its surface is a dense tapestry of overlapping scars, craters left by billions of years of cosmic bombardment. Mercury and Mars tell a similar story. Yet Earth, a much larger target moving through the same celestial neighborhood, presents a deceptively smooth face. This tranquility is an illusion. Our planet has been struck just as often, and just as violently, as its neighbors. The story of Earth’s impact history is not one of absence, but of erasure.

Unlike the geologically quiet Moon, Earth is a dynamic, living world. Its surface is in a constant state of renewal. Tectonic plates drift and collide, thrusting up mountains and subducting entire continents. Volcanoes pave over landscapes with fresh lava. Wind and water relentlessly erode rock, grinding down mountains and filling in basins. These processes, the very signs of a geologically active planet, are also powerful forces of destruction for the fragile evidence of extraterrestrial impacts. Most craters that have formed over Earth’s 4.5-billion-year history have been obliterated, buried, or weathered into ambiguity.

This makes the impact craters that survive within the United States exceptionally valuable. They are not merely geological curiosities; they are rare survivors, precious records of catastrophic events that have punctuated our planet’s history. From the perfectly preserved bowl of Arizona’s Barringer Crater to the deeply buried giant beneath Chesapeake Bay, each site is a geological crime scene. The evidence may be weathered and the trail may be cold, but the clues remain for those who know how to read them. The study of these features is a form of planetary detective work, piecing together a story from microscopic mineral fractures, continent-spanning debris fields, and subtle gravitational anomalies.

This article embarks on a journey through these American impact sites. It begins with the fundamental science of how a hypervelocity collision with an asteroid or comet carves a crater into the Earth, and the specialized toolkit geologists use to distinguish these cosmic scars from more mundane terrestrial features. It then proceeds on a detailed tour across the country, exploring the unique stories and scientific lessons of each crater – from the iconic and visible to the hidden and economically vital. Finally, it will place these events in a broader context, examining the role of impacts in the history of life and the modern efforts to watch the skies and protect our future from a similar fate. The story of America’s impact craters is a story of cosmic violence and geological survival, a narrative that connects the deepest reaches of space with the ground beneath our feet.

The Anatomy of an Impact

The creation of an impact crater is an event of almost unimaginable speed and violence. It is not a simple collision but a hypervelocity explosion that releases energy on a scale that dwarfs human experience. The process transforms both the incoming object and the terrestrial landscape in a fraction of a second, leaving behind a scar whose final shape is a frozen snapshot of a battle between explosive force and gravity. Understanding this process is the first step in learning to read the stories written in these ancient wounds.

From Space Rock to Earth-Shattering Event

The agents of these cosmic collisions are asteroids and comets, small worlds that are leftovers from the birth of the solar system. Asteroids are primarily rocky or metallic objects, most of which orbit the Sun in the main asteroid belt between Mars and Jupiter. They are remnants of planetary formation, chunks of material that never coalesced into a larger body. Comets, in contrast, are icy bodies composed of frozen gases, rock, and dust. They originate in the cold, distant reaches of the solar system, in regions known as the Kuiper Belt and the Oort Cloud. While asteroids are the most common type of impactor to strike Earth, comets also pose a threat, and they tend to arrive with much higher velocities.

The destructive potential of an impactor is not primarily determined by its size, but by its kinetic energy. An object’s kinetic energy increases with the square of its velocity, meaning that doubling the speed quadruples the energy. Objects from space typically hit Earth at about 20 kilometers per second, a speed so immense that the impactor carries more energy, gram for gram, than TNT. An asteroid traveling at this speed produces a crater approximately 20 times larger in diameter than the object itself.

When an impactor strikes, its immense speed means the collision behaves less like a conventional impact and more like a massive explosion. The energy is transferred into the ground almost instantaneously, generating a powerful shock wave that propagates through the target rock. This shock wave is the primary engine of crater formation, responsible for excavating the cavity and fundamentally altering the rocks it passes through. The composition of the impactor, whether a dense iron-nickel asteroid or a less dense icy comet, influences the specifics of the impact, but in all cases, the hypervelocity nature of the event is what makes it a crater-forming explosion.

The Three Stages of Creation

The formation of an impact crater, from the first touch of the impactor to the final settling of the landscape, is a rapid and complex process. For simplicity, scientists divide this continuous event into three distinct stages: contact and compression, excavation, and modification.

The first stage, contact and compression, begins the moment the impactor makes contact with the planet’s surface. Because the object is moving so fast, its rear continues to travel a significant distance while its front is decelerating, causing the impactor to be catastrophically compressed to extreme densities and pressures. Simultaneously, a powerful shock wave is generated, which spreads out from the point of impact into both the target rock and the impactor itself. This initial shock wave compresses and deforms the material, generating immense heat and pressure. This entire stage is incredibly brief, lasting only a few microseconds for a large impact.

The second stage, excavation, follows immediately. The highly compressed and superheated rock, having been subjected to pressures far beyond its material strength, rapidly depressurizes in a violent explosion. This explosion is what carves out the crater. Material is displaced downward and outward, creating a growing bowl-shaped hole known as the transient cavity. A significant portion of the target rock, and most of the impactor, is melted or even vaporized. This material is ejected from the rapidly expanding cavity at high speeds, spraying out in all directions to form an ejecta blanket around the crater. This stage is also very short; for a crater a few kilometers in diameter, the excavation is complete in a matter of seconds.

The final stage is modification and collapse. The transient cavity created during the excavation stage is gravitationally unstable. Its steep walls cannot support their own weight. In this final phase, gravity takes over. The unstable parts of the crater begin to collapse inward. For relatively small impacts, this modification is minor, consisting of loose debris sliding down the crater walls to partially fill the floor. For larger impacts, this stage is far more dramatic and fundamentally alters the crater’s appearance. The walls slump inward in large blocks, and the crater floor, which was pushed down and compressed by the shock wave, rebounds upward. This entire process, from initial contact to the end of modification, is remarkably fast. Even a large, 100-kilometer-diameter crater can form in less than an hour. The result is a permanent geological structure, a scar left by a momentary, catastrophic release of cosmic energy.

Simple Scars and Complex Wounds

The final appearance of an impact crater depends largely on the energy of the impact and the subsequent battle between the explosive force and gravity. This leads to two primary classifications of craters: simple and complex.

Simple craters are the result of smaller, lower-energy impact events. They are characterized by a smooth, bowl-shaped depression with a raised rim composed of uplifted and overturned rock layers. The floor of a simple crater is typically filled with a lens of broken and shattered rock, known as breccia, that slumped back into the cavity during the modification stage. These craters are relatively deep for their size, with a typical width-to-depth ratio of about five to one. The iconic Barringer Crater in Arizona is a classic, well-preserved example of a simple crater. On Earth, the transition from simple to complex craters begins at diameters of about 2 kilometers in soft sedimentary rocks and about 4 kilometers in stronger crystalline rocks.

Complex craters form from larger, higher-energy impacts where the transient cavity is so large that it becomes highly unstable and undergoes significant gravitational collapse. This modification stage creates a much more intricate structure. Instead of a simple bowl, complex craters are proportionally shallower, with width-to-depth ratios closer to thirty to one, and they exhibit several key features.

One of the most prominent features is a central uplift, which can take the form of a single mountain or a cluster of peaks rising from the crater floor. This is not simply a pile of rubble; it is the result of the deep rock beneath the impact site, which was elastically compressed by the shock wave, rebounding upward once the pressure was released. The rock within this central peak is intensely fractured, faulted, and often shows the most significant evidence of shock metamorphism, as it represents material that has been uplifted from great depths.

The inner walls of a complex crater are also different. Instead of a smooth slope, they are marked by a series of step-like terraces. These form as large, crescent-shaped blocks of the crater rim slump downward and rotate backward into the cavity. This slumping process significantly widens the final crater diameter compared to the initial transient cavity.

With increasing impact energy, the central peak itself can become unstable and collapse outward, forming a peak ring – a rugged circle of mountains inside the main crater rim. Even larger impacts can create multi-ring basins, which feature multiple concentric rings of uplifted rock.

The material ejected from a complex crater also differs. The ejecta blanket often has a rumpled, hilly appearance and may show radial lines and grooves, evidence of violent outward flow along the ground. This process can also throw out large blocks of rock that create their own smaller impact sites, known as secondary craters, which can form chains or clusters extending far from the primary impact. The transition from a simple bowl to a complex structure with central peaks and terraced walls is a direct reflection of the scale of the impact. It marks the point where gravity’s relentless pull overwhelms the material strength of the rock, reshaping the initial explosive scar into a more stable, and more complex, final form.

The Geologist’s Toolkit: Finding Hidden Craters

Identifying a circle on a map or an aerial photograph is the easy part. Proving that it was formed by a hypervelocity impact is a rigorous scientific process. Earth’s surface is full of “cryptoexplosion structures” – circular features of uncertain origin. Geologists have had to develop a specialized toolkit of diagnostic criteria to distinguish true impact craters from features created by more common terrestrial processes like volcanism, salt dome uplift, or simple erosion. Confirmation relies on finding the unique fingerprints left behind by the extreme physics of an impact event, evidence that can range from microscopic alterations in mineral crystals to continent-spanning chemical anomalies.

Reading the Rocks: Shock Metamorphism

The most definitive evidence for an impact origin is found at the microscopic level. When a hypervelocity impactor strikes, it generates a shock wave that propagates through the target rocks at supersonic speeds. The pressures within this wave are immense, reaching hundreds of gigapascals – far beyond anything produced by normal geological processes like volcanic eruptions or tectonic faulting. This intense, near-instantaneous pulse of pressure and heat permanently alters the crystal structure of minerals in the target rock, a process known as shock metamorphism. These alterations are the “smoking gun” that geologists seek to confirm an impact.

The most famous and reliable of these shock effects are planar deformation features (PDFs). These are microscopic, parallel sets of glassy lamellae that form within the crystal lattice of minerals like quartz and feldspar. They are not random fractures; their orientation is precisely controlled by the mineral’s crystal structure. Multiple sets of PDFs with different crystallographic orientations can be found within a single grain. Critically, PDFs are only known to be produced by the extreme shock pressures of an impact event. They are not found in rocks from volcanic environments or tectonic fault zones, making their presence an unambiguous indicator of an impact.

The immense pressures can also transform minerals into new, denser forms, or high-pressure polymorphs. The discovery of two such polymorphs of silica (silicon dioxide) at Barringer Crater in the 1960s was a landmark moment in geology. Scientists identified coesite and, subsequently, stishovite in the shocked sandstone. While coesite can occasionally form in deep-Earth tectonic settings, stishovite is only known to form naturally in impact structures. Its discovery provided irrefutable proof that the crater was formed by a hypervelocity impact. Other high-pressure minerals, such as reidite (a polymorph of zircon) and even microscopic diamonds formed from carbon in the target rocks, also serve as impact indicators.

Other microscopic clues include planar fractures (parallel sets of open cracks in minerals, which are common but can be intensely developed at impact sites), distinctive forms of crystal twinning, and the creation of diaplectic glass. This is a peculiar type of glass, also known as thetomorphic glass, where a mineral like quartz is transformed into an amorphous state by shock pressure without ever melting. The original shape and texture of the mineral grain are preserved, but its internal crystal structure is gone. The search for these shock-metamorphic effects, often requiring painstaking analysis of rock samples with powerful microscopes, forms the basis for confirming a suspected impact structure.

The Cones of Cataclysm: Shatter Cones

While most definitive impact evidence is microscopic, one feature provides macroscopic, naked-eye proof of a hypervelocity shock event: the shatter cone. These are distinctive, conical fracture patterns that form in the bedrock beneath an impact crater. They are characterized by a unique “horsetail” pattern of fine grooves, or striae, that radiate outwards from the cone’s apex. Shatter cones can range in size from centimeters to several meters long, and often occur in nested, cone-on-cone arrangements.

Shatter cones are only known to form under the specific shock pressures generated by a meteorite impact or a large nuclear explosion, typically in the range of 2 to 30 gigapascals. They are considered unequivocal evidence that the rock has been subjected to a powerful shock wave. The formation mechanism is still debated, but it is thought to involve the interaction of the shock wave with inhomogeneities in the rock, creating a network of branching fractures.

In the field, shatter cones are an invaluable tool for geologists. Because the apex of the cone generally points toward the source of the shock wave – upward and toward the center of the impact – their orientation can be used to map out the geometry of a crater and locate its center, even if the structure is heavily eroded. They are most commonly found in the central uplifts of complex craters, where deeply buried and intensely shocked rock has been brought to the surface.

Identifying shatter cones requires a trained eye. They can be poorly developed in coarse-grained rocks and can be confused with other geological features. Sedimentary structures called cone-in-cone and striated fracture surfaces from faulting, known as slickensides, can sometimes mimic their appearance. However, true shatter cones have a distinctive set of features, including the branching horsetail striations and their penetrative nature, forming through the rock regardless of its original layering. The discovery of shatter cones at a suspected site is often the first major breakthrough that elevates it from a “possible” to a “probable” impact structure, prompting the more detailed microscopic analysis needed for final confirmation.

Beyond the Visible: Geophysical and Geochemical Clues

A great number of impact craters in the United States, particularly in the stable interior of the continent, are not visible at the surface. They lie buried beneath hundreds or thousands of meters of younger sedimentary rock or glacial deposits. Finding and studying these hidden structures requires geologists to look beneath the surface using geophysical techniques and to search for the far-flung chemical fingerprints of the impactor.

Geophysical surveys are essential for “seeing” buried structures. Gravity surveys measure minute variations in the Earth’s gravitational field. Because an impact shatters and fractures rock, the breccia that fills a crater is typically less dense than the surrounding undisturbed rock. This zone of lower density creates a negative gravity anomaly – a region of slightly weaker gravity – that can reveal the circular outline of a buried crater. Conversely, the central uplifts of complex craters often bring denser, deeper rocks closer to the surface, creating a positive gravity anomaly in the center. The combination can produce a distinctive “bullseye” pattern, which was instrumental in identifying the giant Chicxulub crater.

Magnetic surveys work on a similar principle, mapping variations in the Earth’s magnetic field. An impact can disrupt or alter the magnetic properties of basement rocks, again creating a circular anomaly that stands out from the surrounding geology. The most powerful tool is seismic reflection profiling. This technique, widely used in oil and gas exploration, involves sending sound waves into the ground and recording the echoes that bounce back from different rock layers. The resulting data can be used to create a 2D or 3D image of the subsurface geology, clearly revealing the disturbed layers, faults, central uplift, and breccia lens characteristic of an impact structure. Many of the buried craters in the U.S. Midwest and Great Plains were discovered precisely because these anomalous structures were identified on seismic data collected during the search for hydrocarbons.

Geochemical clues provide another powerful method for linking a geological event to an impact. The most famous example is the iridium anomaly. Iridium is a platinum-group element that is very rare in Earth’s crust but is relatively abundant in many types of asteroids. The discovery of a thin, global layer of clay enriched in iridium at the Cretaceous-Paleogene boundary was the key piece of evidence that linked the extinction of the dinosaurs to a massive asteroid impact. Finding such an elemental signature in impact melt rocks within a crater can help confirm its origin and even identify the type of impactor.

Other geochemical tracers include tektites and impact spherules. These are small, droplet-shaped bodies of natural glass that form when target rock is melted and flung high into the atmosphere, cooling and solidifying as it falls back to Earth. These glassy beads can be scattered over immense areas known as strewn fields, sometimes thousands of kilometers from the source crater. The North American tektite strewn field, which covers a vast portion of the Atlantic coast and the Gulf of Mexico, is now known to be ejecta from the Chesapeake Bay impact crater. By tracing these cosmic breadcrumbs back to their source, geologists can uncover the location of ancient, hidden impacts.

A Tour of America’s Impact Craters

The United States is home to a remarkable collection of impact structures, showcasing a wide range of sizes, ages, and states of preservation. From the fresh, iconic bowl of Barringer Crater to the deeply buried and economically significant structures of the Great Plains, each site tells a unique story of cosmic collision and geological persistence. While the global tally of confirmed impact craters approaches 200, the U.S. holds a significant fraction, many of which have played pivotal roles in advancing our understanding of impact processes.

This tour explores the most significant of these sites, categorized by their geological characteristics, historical importance, and scientific contributions. The journey begins with the most famous craters, digs into those hidden beneath the surface, and concludes with structures that remain subjects of ongoing scientific debate. The following table provides a comprehensive overview of the confirmed and probable impact structures across the country, serving as a reference for the detailed explorations that follow.

The Icon of the Desert: Barringer Crater, Arizona

In the arid expanse of northern Arizona, about 37 miles east of Flagstaff, lies the most famous and best-preserved impact crater on Earth. Barringer Crater, also known as Meteor Crater, is a stark and breathtaking sight: a nearly perfect bowl-shaped depression, 1.2 kilometers (about 0.75 miles) across and 170 meters (560 feet) deep, with a rim rising 45 meters above the surrounding plain. Its youthful age – a mere 50,000 years – and the dry climate have protected it from the erosional forces that have erased so many other terrestrial craters, making it the quintessential example of a simple impact structure. Its story is not just one of geological violence, but also of a scientific revolution that changed how we view our planet and the solar system.

When American settlers first encountered the crater in the 19th century, its origin was a mystery. The prevailing scientific view, championed by Grove Karl Gilbert, the chief geologist for the U.S. Geological Survey, was that it must have been formed by a volcanic steam explosion. Gilbert investigated the crater in 1891, reasoning that if it were an impact crater, a massive iron meteorite – the parent body of the thousands of metallic fragments found scattered for miles around – must be buried beneath its floor. When his magnetic surveys failed to detect a large buried mass, he concluded the volcanic hypothesis was more likely.

This conclusion was famously challenged by Daniel M. Barringer, a Philadelphia mining engineer. In 1903, convinced of the crater’s cosmic origin, he and his partners acquired the land through mining claims. Barringer was driven by a dual motivation: scientific curiosity and the prospect of a colossal fortune. He believed, like Gilbert, that a massive meteorite was buried there, and he spent 26 years and a considerable fortune drilling shafts and boreholes in an attempt to locate and mine what he thought would be a billion-dollar lode of nickel-iron. He never found his buried treasure – we now know that most of the impactor vaporized on impact – but his relentless work laid the foundation for proving the crater’s true origin. He meticulously documented the pulverized rock, the random mixture of meteorite fragments within the ejecta, and the fact that the rock layers of the rim were overturned, all powerful evidence of a catastrophic impact from above.

The definitive proof came decades after Barringer’s death. The scientific community’s view had been slowly shifting, but the landmark discoveries came in the 1960s with the advent of shock metamorphism as a diagnostic tool. Researchers Eugene Shoemaker and Edward C. T. Chao studied samples from the crater and identified the high-pressure silica minerals coesite and stishovite. These minerals can only be formed under the immense, instantaneous pressures generated by a hypervelocity impact, pressures far exceeding those in any volcanic process. This discovery was the “smoking gun.” It not only vindicated Barringer’s decades-old theory but also established a new, definitive criterion for identifying impact structures worldwide. Barringer Crater became the type-specimen, the first location on Earth where an impact origin was unequivocally proven through the discovery of shock-metamorphic minerals.

The impact event itself occurred during the Pleistocene epoch, when the climate of the Colorado Plateau was cooler and wetter. A juniper-pinyon woodland covered a landscape roamed by mammoths, giant ground sloths, and camels. Into this world streaked a 50-meter-wide iron-nickel asteroid, weighing some 300,000 tons and traveling at a speed of about 12 kilometers per second (over 26,000 miles per hour). The resulting explosion had the force of more than 2.5 million tons of TNT, blasting 175 million tons of rock out of the ground.

The target geology consisted of a sequence of nearly flat-lying sedimentary rocks: the reddish Moenkopi mudstone at the surface, overlying the Kaibab dolomite and the Coconino sandstone. The force of the explosion excavated these layers and threw them outward, creating an ejecta blanket that surrounds the crater. In a classic demonstration of impact mechanics, these layers were overturned in the process, creating an “inverted stratigraphy” in the crater rim where the oldest layer, the Coconino sandstone, lies on top of the youngest, the Moenkopi formation.

The environmental effects, though localized, would have been catastrophic. A blinding fireball and a searing thermal pulse would have ignited vegetation for kilometers. An air blast with winds exceeding 1,000 kilometers per hour would have scoured the landscape clean near the crater and flattened trees for up to 19 kilometers in every direction. Any animal within 3 to 4 kilometers of ground zero would have been killed instantly by the shockwave, with severe injuries extending out for more than 20 kilometers.

In the 1960s and 1970s, this stark, well-preserved landscape found a new purpose. Recognizing its resemblance to the cratered surface of the Moon, NASA used Barringer Crater as a primary training ground for the Apollo astronauts. Geologists like Eugene Shoemaker led the future moonwalkers on field exercises within the crater, teaching them the principles of impact geology, how to identify different rock types in a complex terrain, how to conduct radial sampling traverses, and how to navigate the challenging topography of a cratered landscape. Every astronaut who walked on the Moon trained in northern Arizona, and the lessons learned in the bowl of Barringer Crater were directly applied to the exploration of Hadley Rille and Descartes Highlands. The crater that revolutionized our understanding of Earth’s geology also played a direct role in humanity’s first steps onto another world.

The Sunken Giant: The Chesapeake Bay Impact Crater

For millions of years, the largest impact crater in the United States lay hidden, buried deep beneath the sediments of the Atlantic Coastal Plain. Its existence was a significant secret, influencing the flow of rivers, the salinity of groundwater, and the very shape of the coastline, all while remaining completely unseen. The discovery of the Chesapeake Bay impact crater in the late 20th century was a geological revelation, uncovering a sunken giant that continues to shape the environment of the Eastern Seaboard today.

The first clues were subtle and enigmatic. For over a century, well drillers in southeastern Virginia had been puzzled by a zone of unusually briny groundwater. As far back as 1864, Union soldiers drilling a well at Fort Monroe encountered salty water where fresh aquifers were expected. This deep saltwater anomaly remained a local hydrogeological mystery for decades. The story began to unfold in 1983, when geologists studying a deep-sea drilling core taken off the coast of Atlantic City, New Jersey, discovered a strange, 20-centimeter-thick layer of ejecta. It contained tektites and shocked minerals, clear evidence of a major impact event somewhere on the North American East Coast, but the source crater was unknown.

The final piece of the puzzle fell into place a decade later. In 1993, seismic reflection data, originally collected for oil exploration by Texaco, was re-examined by scientists at the U.S. Geological Survey. The data revealed an astonishing structure buried 300 to 500 meters beneath the mouth of the Chesapeake Bay: a massive, 85-kilometer (53-mile) wide circular feature with all the hallmarks of a complex impact crater. The mysterious ejecta layer and the anomalous saltwater had found their source.

The impact occurred about 35.5 million years ago, during the late Eocene epoch. At that time, sea levels were high, and the shoreline was near modern-day Richmond, Virginia. A bolide – an asteroid or comet estimated to be 3 to 5 kilometers wide – slammed into the shallow waters of the continental shelf. The impact was cataclysmic. It tore through the overlying water and hundreds of meters of soft marine sediments, striking the hard granitic basement rock below.

The resulting structure is a classic complex crater, often described as having an “inverted sombrero” shape. It consists of a deep, 38-kilometer-wide inner basin, which is filled with a thick lens of shattered and melted rock known as impact breccia. Surrounding this is a crystalline peak ring, formed from the rebound of the deep basement rock. Beyond the peak ring lies a relatively flat-floored annular trough, which is in turn bounded by a faulted and collapsed outer rim that defines the crater’s full 85-kilometer diameter.

The consequences of this event are still felt today. The most significant is the disruption of the region’s hydrogeology. The impact completely destroyed the layered sequence of coastal plain aquifers. In their place, it left a single, massive reservoir of breccia, a jumbled mass of porous rock fragments. This reservoir is filled with ancient, highly saline water that is roughly 1.5 times saltier than modern seawater. This hypersaline body of water is the source of the salty groundwater that had puzzled geologists for so long. Its presence limits the availability of fresh water in the lower Chesapeake region and poses a risk of contamination to the overlying freshwater aquifers, especially along faults that cut through the post-impact sediments.

Another lasting effect is land subsidence. The breccia that fills the crater is less compacted than the surrounding crystalline rock and undisturbed sediments. Over the 35 million years since the impact, this thick pile of rubble has been slowly compacting under the weight of overlying sediments. This causes the land surface directly above the crater to sink, a process that continues today. This localized subsidence exacerbates the effects of regional sea-level rise, making the Chesapeake Bay area one of the most vulnerable hotspots for coastal flooding and shoreline erosion on the Atlantic coast.

The crater’s buried topography even guided the formation of the modern Chesapeake Bay. The bay itself is a much younger feature, formed when rising sea levels at the end of the last ice age flooded the ancient valley of the Susquehanna River. The path of this river and its major tributaries, like the James and York rivers, was influenced by the subtle, long-lasting topographic depression created by the underlying impact structure. The lower courses of the James and York rivers make abrupt turns to the northeast, following the curve of the crater’s buried outer rim. In essence, the ancient impact created a basin that predetermined where the modern bay would eventually form millions of years later. As one of the best-preserved large marine impact craters on Earth, the Chesapeake Bay structure is a vital natural laboratory for scientists studying the unique physics of impacts into water and their long-term geological and environmental consequences.

Echoes of Extinction: The Chicxulub Legacy in the United States

Approximately 66 million years ago, an asteroid between 10 and 15 kilometers wide slammed into the shallow waters off the Yucatán Peninsula, triggering one of the most severe mass extinctions in Earth’s history. The impact excavated the Chicxulub crater, a massive structure some 180 kilometers in diameter. While the crater itself lies buried beneath Mexico and the Gulf of Mexico, the cataclysmic effects of this event radiated across the globe, leaving an indelible mark on the geological record of the United States. The U.S. holds some of the world’s most important sites for studying the immediate and devastating aftermath of the impact that ended the age of dinosaurs.

The most widespread evidence is the Cretaceous-Paleogene (K-Pg) boundary layer. This is a thin, distinct layer of clay and sediment found in rocks of the correct age all over the world. In the United States, well-preserved K-Pg boundary sections are exposed in places like Big Bend National Park in Texas, Trinidad Lake State Park in Colorado, and numerous sites in Mississippi, Alabama, and New Jersey. This layer is the geological tombstone for the Mesozoic Era. Geochemically, it is defined by a sharp spike in the concentration of iridium, an element rare in Earth’s crust but common in asteroids. This iridium anomaly was the first clue, discovered in the 1980s, that linked the mass extinction to an extraterrestrial impact.

The U.S. boundary layers contain more than just iridium. They are often rich in other impact-related materials that paint a picture of the event. These include shocked quartz grains, their crystal lattices scarred with the microscopic planar deformation features that serve as definitive proof of a hypervelocity impact. Also present are impact spherules and tektites, tiny beads of glass that formed from droplets of molten rock blasted into the atmosphere, which then rained back down across the continent. In some locations, this layer also contains a spike in fern spores, a classic sign of a “fern spike” that indicates the widespread devastation of flowering plants and the subsequent colonization of the barren landscape by opportunistic ferns.

Because of its proximity to the impact site, the southern United States bears the scars of some of the most violent immediate effects. The impact in the shallow Gulf of Mexico generated a mega-tsunami of almost unimaginable scale. Models suggest the initial waves may have been over 100 meters high as they radiated across the Gulf. This colossal wave scoured the seafloor and crashed into the coastlines of what are now Texas, Louisiana, Alabama, and Mississippi.

The geological evidence for this mega-tsunami is dramatic. Along the Brazos River in Texas, geologists have found a thick, chaotic deposit of jumbled sandstone blocks, mud clumps, and marine fossils sandwiched within otherwise fine-grained marine shales. This deposit represents debris ripped from the seabed and coastline by the tsunami’s incredible force and deposited far inland. Similar tsunami deposits are found throughout the Gulf Coast region, marking the violent inundation of the continent. In Cuba, deposits from the event include boulders the size of houses.

The impact also generated a mega-earthquake, estimated to have been magnitude 10 or greater, that shook the entire planet. The seismic waves would have been particularly intense across North America. In K-Pg sections from Texas to Colombia, scientists have documented widespread evidence of intense soft-sediment deformation, liquefaction, and bed disruption. These features indicate that the ground was violently shaking for weeks or even months following the impact, as the Earth rang like a bell from the colossal collision.

The Chicxulub impact was a global event, but the geology of the United States provides a uniquely detailed, ringside view of its immediate, continent-shattering consequences. From the fine layer of impactor dust that settled over the Rocky Mountains to the jumbled tsunami debris on the Gulf Coast, the rocks preserve a vivid record of the day the world changed forever.

The Buried Treasures of the Plains: Craters and Hydrocarbons

While many impact craters are objects of purely scientific interest, a significant number of those in the United States have a surprising economic importance. The same violent processes that shatter and deform rock during an impact can also create ideal conditions for the formation of hydrocarbon reservoirs. The intense fracturing and brecciation of the target rock can generate substantial porosity (open space) and permeability (connectedness of spaces), turning otherwise dense rock into a natural trap for oil and gas. In North America, roughly half of the known impact structures located in sedimentary basins have been found to host commercial oil and/or gas fields, transforming these ancient scars into valuable energy resources.

The primary trapping mechanisms are related to the complex structure of the craters. In a complex crater, the central uplift brings deeply buried and highly fractured rock closer to the surface. The faulted and slumped blocks along the crater’s rim can also form effective traps. If these fractured zones are located in a region where source rocks have generated hydrocarbons, the crater structure can act as a natural reservoir, collecting oil and gas that migrates into it. Many of these productive craters are buried deep underground and were discovered not by crater-hunters, but by geologists exploring for fossil fuels.

Ames Crater, Oklahoma: The story of the Ames crater is a classic example of an accidental, and highly profitable, discovery. For years, oil companies drilled around the area in Major County, Oklahoma, with little success. Then, in 1991, Rex Olson, an exploration manager for Continental Resources, was examining seismic data of the region. He noticed a strange, circular anomaly about 16 kilometers (10 miles) in diameter that he described as looking like a “cow track in the mud.” He and company CEO Harold Hamm recognized the pattern as a possible astrobleme, or “star wound.” Despite skepticism in the industry that such features could be productive, they decided to drill directly into the center of the buried structure.

The well was a success, striking a prolific reservoir of oil and gas. The impact, which occurred approximately 470 million years ago in a shallow Ordovician sea, had shattered the dense Arbuckle Dolomite. The central uplift of the complex crater was composed of this highly fractured dolomite, creating an exceptional reservoir. Since its discovery, the Ames crater has become one of the most productive impact-related fields in the country, yielding over 17 million barrels of oil and nearly 80 billion cubic feet of natural gas.

Red Wing Crater, North Dakota: Located in the petroleum-rich Williston Basin, the Red Wing crater is another major hydrocarbon producer. Discovered in 1972, this 9-kilometer-diameter structure is buried about 2,000 meters below the surface. The impact, which occurred around 200 million years ago, created a complex crater with a prominent central uplift. Drilling into this central peak revealed a startling geological situation: the normally horizontal layers of Mississippian-age carbonate rocks were tilted on their sides, creating an oil column that was an astonishing 870 meters thick, compared to the typical 30 meters in the region. This thick, highly fractured reservoir has been immensely productive, with ultimate recovery estimated to be as high as 60 million barrels of oil. The impact origin was definitively confirmed in 1996 with the discovery of planar deformation features in quartz from drill core samples.

Newporte Crater, North Dakota: Also in the Williston Basin, near the Canadian border, lies the smaller Newporte crater. This 3.2-kilometer-diameter structure was discovered during oil exploration in 1977. Unlike Ames and Red Wing, where production is concentrated in the central uplift, the Newporte field produces oil and gas from the brecciated Precambrian basement rocks that form the crater’s raised peripheral rim. The impact, which happened nearly 500 million years ago, fractured these ancient crystalline rocks, creating a unique trap along the crater’s edge. The discovery of shocked quartz and feldspar in drill cores later confirmed its impact origin.

These craters, along with others like Avak in Alaska and Calvin in Michigan, demonstrate a powerful connection between catastrophic cosmic events and the formation of valuable terrestrial resources. The search for oil and gas has inadvertently become one of the most effective methods for discovering buried impact structures, turning these ancient wounds into hidden treasures.

Scars on the Heartland: A Midwestern Tour

The stable geological heartland of North America, a vast region of flat-lying sedimentary rocks known as the interior craton, has been a particularly effective preserver of ancient impact structures. While tectonic forces on the continent’s margins have folded, faulted, and eroded many craters into oblivion, the Midwest’s relative tranquility has allowed numerous impact scars to survive, often protected by a thick blanket of younger sediments. This has made the region a hotspot for crater discovery, often as a byproduct of the search for water or hydrocarbons. This tour explores the significant impact sites scattered across the plains and Great Lakes region.

Deep beneath the cornfields of Iowa lie two of the country’s most scientifically interesting craters. The Manson impact structure, near the town of Manson, is a large, 35-kilometer-wide complex crater buried under about 30 to 90 meters of glacial till. Its existence was first hinted at in 1912, when drillers for a town well encountered unusual, deformed crystalline rocks instead of the expected sedimentary layers, and found the only naturally soft water in the state. For decades it was considered a “cryptovolcanic structure.” In the 1960s, the discovery of shocked quartz grains confirmed its impact origin. The impact occurred about 74 million years ago, and for a time, Manson was a leading candidate for the impact that caused the extinction of the dinosaurs. However, more precise radiometric dating later proved it was about 10 million years too old. It remains one of the largest and best-preserved complex craters in the United States.

Iowa’s Buried Giants: Manson and Decorah

To the northeast, buried beneath the town of Decorah, is a smaller and much older crater. The 5.6-kilometer-wide Decorah crater was formed by an impact about 470 million years ago. Its existence was confirmed in 2013 through geological mapping and geophysical surveys. The crater is remarkable because the anoxic, low-energy basin created by the impact provided an ideal environment for the preservation of fossils. The Winneshiek Shale, which fills the crater, is a Lagerstätte – a sedimentary deposit with extraordinary fossil preservation. Scientists have uncovered thousands of exceptionally preserved fossils of soft-bodied marine animals, including the oldest and one of the largest known species of “sea scorpion” (a eurypterid), a seven-foot-long predator named Pentecopterus decorahensis.

Missouri’s 38th Parallel Structures

Stretching across southern Missouri is an enigmatic alignment of geological anomalies known as the 38th parallel structures. This 700-kilometer-long lineament includes at least seven circular disturbances, sparking a tantalizing but controversial hypothesis: that they could be the remnants of a serial impact, caused by a fragmented comet or asteroid striking the Earth in a linear chain, similar to the Shoemaker-Levy 9 impact on Jupiter.

Two of the structures on this lineament are confirmed impact craters. The Crooked Creek crater is a 7-kilometer-wide, deeply eroded complex crater with a distinct central uplift. Its impact origin is confirmed by the presence of both shatter cones and planar deformation features in quartz. The Decaturville crater, about 6 kilometers in diameter, is another exposed complex structure with a central uplift containing shatter cones and shocked quartz. However, the serial impact hypothesis remains debated. The ages of the craters are not precisely aligned, and other features on the lineament, like Hicks Dome in Illinois, are now believed to be volcanic in origin. Nonetheless, the concentration of confirmed and suspected impacts along this line remains a fascinating geological puzzle.

The Great Lakes Cluster

The states surrounding the Great Lakes host a number of confirmed impact structures. In Illinois, both the Des Plaines and Glasford craters are buried structures discovered through drilling. The 8-kilometer Des Plaines structure, beneath a suburb of Chicago, was first noted by well drillers in the 1890s. Its impact origin was confirmed by the discovery of shatter cones in drill cores. The smaller 4-kilometer Glasford crater was found during drilling for natural gas storage and was also confirmed by the presence of shatter cones.

In Indiana, the Kentland crater is a deeply eroded complex structure about 13 kilometers in diameter. While mostly covered by glacial till, quarrying operations have exposed the crater’s central uplift, revealing intensely deformed and nearly vertical beds of rock that have been raised over 600 meters from their original depth. The presence of abundant shatter cones confirms its impact origin, though its age remains poorly constrained to sometime in the last 97 million years.

Michigan is home to the Calvin crater, an 8.5-kilometer-wide buried structure discovered in 1987 from test well data. It has the classic morphology of a complex crater, with a central dome, an annular depression, and an outer rim. While definitive shock-metamorphic features have not been identified, the presence of microbreccias and its structural characteristics strongly support an impact origin.

Wisconsin has two confirmed exposed craters. The Rock Elm structure, 6 kilometers in diameter, is a deeply eroded crater where the impact origin was confirmed by the discovery of shocked quartz with planar microstructures. It gained further significance with the identification of reidite, a rare high-pressure polymorph of zircon, making it only the fourth site on Earth where this mineral has been found. The Glover Bluff crater, about 8 kilometers across, is a more poorly understood structure. Its impact origin was confirmed by the discovery of shatter cones, but it remains one of the most under-researched exposed craters in the country.

The Ordovician Meteor Event

A number of these Midwestern craters – including Ames in Oklahoma, Decorah in Iowa, and Rock Elm in Wisconsin – date to the Middle Ordovician period, roughly 470 million years ago. Their similar ages have led scientists to propose the Ordovician meteor event. This theory suggests that for a period of a few million years, the rate of meteorite impacts on Earth increased dramatically. This spike in impacts is thought to have been caused by the catastrophic collision and breakup of a large, 150-kilometer-wide asteroid in the main belt. This event would have sent a shower of fragments into Earth-crossing orbits, leading to a temporary but intense period of bombardment, the scars of which are preserved in the ancient rocks of the American heartland.

Mountain and Basin Impacts: From Appalachia to the West

While the stable craton of the Midwest has preserved a rich record of buried impact structures, craters are also found in the more geologically complex terrains of the United States, from the ancient Appalachian Mountains to the rugged basins and ranges of the West. These structures are often exposed at the surface, but they are typically much more heavily eroded and sometimes deformed by subsequent tectonic activity, presenting a different set of challenges and insights for geologists.

Appalachian Impacts

The city of Middlesboro, Kentucky, holds the unique distinction of being built almost entirely inside a 6-kilometer-wide impact crater. Nestled within the Appalachian Mountains, the circular basin was long considered a simple geological depression. In the 1960s the discovery of shatter cones and other shock-metamorphic evidence, like planar deformation features in quartz, confirmed its origin as a complex impact structure formed less than 300 million years ago. Today, the bowl shape of the basin is clearly visible from the Pinnacle Overlook at Cumberland Gap National Historical Park.

Further east, in southern Ohio, lies the Serpent Mound structure. This 8- to 14-kilometer-wide feature is a deeply eroded complex crater with a prominent central uplift. Its origin was debated for over a century, with early geologists terming it a “cryptoexplosion structure.” The presence of the famous Serpent Mound effigy on the crater’s flank led to speculation that the unusual geology inspired its construction by Native Americans. The impact origin was finally confirmed through the discovery of shatter cones, shocked quartz, and the high-pressure mineral coesite, linking it definitively to a cosmic collision that occurred less than 320 million years ago.

Tennessee’s Twin Craters

Central Tennessee is home to two well-studied, exposed complex craters. The Wells Creek crater, about 12 kilometers in diameter, is a geological anomaly that was noted by railroad surveyors as early as 1855 due to its chaotically deformed rocks. For over a century, its origin was debated between volcanism and impact. The debate was settled in the 1960s when extensive mapping and drilling, funded by NASA, revealed abundant and well-preserved shatter cones in the Knox Dolomite of the central uplift, confirming it as an impact structure approximately 200 million years old. Nearby, the smaller Flynn Creek crater (3.8 kilometers) tells a similar story. Also formed in a shallow sea about 360 million years ago, its impact origin was confirmed by the discovery of shatter cones in its central peak. It has been extensively studied through a USGS drilling program, making it an invaluable analog for understanding the mechanics of small complex craters.

The Texas Trio

Texas hosts three confirmed impact sites, each with a distinct character. The Odessa Meteor Crater, near the city of the same name, is actually a field of at least five small craters, the largest being only 160 meters across. Formed less than 64,000 years ago, it is significant because it is one of the few impact sites in the world where abundant fragments of the impactor – an iron meteorite – were found scattered in and around the craters. This allowed for its relatively early identification as an impact site in the 1920s.

In contrast, the Sierra Madera crater in West Texas is a large, 13-kilometer-wide complex structure. It is deeply eroded, and what remains today is primarily the crater’s central uplift, which forms a prominent, circular range of hills rising nearly 800 feet above the surrounding plains. The uplifted rocks are intensely folded and faulted and contain abundant shatter cones and breccias. Because its structure is so well exposed, Sierra Madera has served as a key terrestrial analog for studying the formation of central peaks in craters on the Moon and Mars.

The Marquez crater, in East Texas, is a 12.7-kilometer-wide buried complex crater. While most of the structure is hidden, its central uplift is partially exposed at the surface as the “Marquez Dome.” It was in these exposed rocks that geologists found shatter cones and microscopic planar deformation features, confirming the 58-million-year-old structure’s impact origin.

Ancient Western Structures

The western United States, with its active tectonic history, contains some of the nation’s oldest and most challenging impact structures to study. The Santa Fe impact structure in New Mexico is an ancient scar, estimated to be over 1.2 billion years old. It is so deeply eroded that only the basement rocks of the crater floor and central uplift remain, exposed in the Sangre de Cristo Mountains. There is no visible crater morphology. Its existence was completely unknown until 2005, when a geologist serendipitously spotted large, well-formed shatter cones in a road cut just northeast of Santa Fe. Subsequent study revealed microscopic shock features, confirming the presence of one of the oldest impact structures in the country.

In Utah’s Canyonlands National Park lies Upheaval Dome, one of the most visually striking and intensely debated geological features in the U.S. This 10-kilometer-wide circular structure consists of a central dome of uplifted and spectacularly eroded rock layers, surrounded by a ring-shaped syncline. For decades, two competing theories dominated the debate over its origin: was it a salt dome, formed by underlying salt deposits pushing upward, or was it the central uplift of a complex impact crater? The proximity to the Paradox Basin salt deposits favored the salt dome hypothesis for many years. However, detailed mapping revealed structural features more consistent with an impact, and the discovery of shocked quartz grains with planar deformation features in the 2000s has tipped the scientific consensus firmly in favor of an impact origin.

The Unconfirmed and the Controversial

The process of confirming an impact crater is rigorous, demanding unambiguous evidence of shock metamorphism. As a result, there are numerous circular structures across the United States that display many characteristics of an impact but lack the definitive “smoking gun” evidence. These “probable” or “potential” sites represent the frontiers of impact crater research, where scientific debate is active and the detective work is ongoing.

Weaubleau Structure, Missouri: As part of the 38th parallel lineament, the Weaubleau structure is a large, roughly 19-kilometer-wide circular feature that is considered a probable impact site. The evidence in its favor is strong: a distinct circular pattern in the region’s drainage, extensive areas of brecciated and deformed rock, and the reported discovery of planar deformation features in quartz grains. The impact is thought to have occurred around 335-340 million years ago into a shallow sea, when the target limestone was still uncemented sediment. Despite the compelling evidence, its full extent is not perfectly mapped, and it has not yet been universally accepted into the ranks of confirmed craters by all databases, highlighting the high bar for absolute confirmation.

Panther Mountain, New York: Hidden beneath the forested peaks of the Catskill Mountains, the Panther Mountain structure is a potential 10-kilometer-wide buried crater. Its existence is inferred primarily from surface topography – the Esopus Creek makes an almost perfectly circular turn, outlining the feature – and from geophysical data. Gravity surveys have revealed a negative gravity anomaly consistent with a buried crater filled with lower-density breccia. Drill cuttings from an old gas well have reportedly yielded shocked quartz and microscopic iron spherules. However, the evidence has not been widely published in peer-reviewed literature, and some geologists remain skeptical, leaving Panther Mountain as an intriguing but unconfirmed candidate.

Johnsonville (Snow’s Island), South Carolina: This 11-kilometer-wide circular feature is buried beneath the coastal plain sediments at the junction of the Pee Dee and Lynches Rivers. It was first identified as a geophysical anomaly from magnetic surveys. Subsequent study of drill cores from the area revealed the presence of impact breccia and petrologic evidence of shock metamorphism, including planar fractures in quartz and diaplectic glass. The evidence strongly suggests an impact origin, likely from the same late Eocene time frame as the nearby Chesapeake Bay impact, but it has yet to be formally added to the primary Earth Impact Database.

Brushy Creek, Louisiana: This small, 2-kilometer-wide circular depression in St. Helena Parish is a much younger candidate, estimated to be only 11,000 to 30,000 years old. The feature was identified from laser imaging of the topography. Petrographic study of sand from its rim revealed intensely fractured and shocked quartz grains, which are not found in the surrounding sediments. While other origins like salt domes or volcanoes have been ruled out for the area, the evidence is still being evaluated by the scientific community.

Victoria Island, California: Discovered during oil exploration, the Victoria Island structure is a 5.5-kilometer-wide circular anomaly buried 1,500 meters beneath the Sacramento-San Joaquin River Delta. Analysis of 3D seismic survey data revealed a structure with a concentric, terraced rim and a central uplift, perfectly matching the morphology of a complex impact crater. Its age is estimated to be between 37 and 49 million years. While the seismic evidence is compelling, it remains a “probable” structure because no drill cores have yet been recovered to provide the direct rock evidence – the shocked minerals – needed for confirmation.

These and other potential sites across the country represent the ongoing nature of scientific discovery. Each one is a geological puzzle, waiting for the right piece of evidence to either confirm its cosmic origin or assign it to a more terrestrial process.

The Bigger Picture: Impacts, Life, and the Future

The study of impact craters in the United States extends far beyond the cataloging of geological scars. These structures provide significant insights into some of the most fundamental questions about our planet: the history of life, the processes that shape our world, and the potential threats we face in the future. They are natural laboratories that reveal the dual nature of impacts as both devastating agents of extinction and potential crucibles for life, and they serve as important data points in the modern effort to defend our planet from future collisions.

Craters as Crucibles and Cataclysms

Impact events have played a powerful and paradoxical role in the history of life on Earth. On one hand, they are agents of mass destruction. The Chicxulub impact is the most famous example, an event that triggered a global environmental collapse and led to the extinction of approximately 75% of all species, including the non-avian dinosaurs. The evidence for this is written in the K-Pg boundary layer found across the United States and the world. Smaller impacts, while not causing global extinctions, still result in complete devastation on a regional scale.

On the other hand, some scientists speculate that impacts may have contributed to the origin and evolution of life. Comets and certain types of asteroids are rich in water and organic molecules, the basic building blocks of life. The period of heavy bombardment in the early solar system could have delivered vast quantities of these essential ingredients to the young Earth. Furthermore, the impact process itself creates unique environments. The immense heat of an impact can generate long-lived hydrothermal systems within the fractured crater structure. These systems, with their circulating hot water and diverse mineralogy, could have provided ideal chemical reactors – warm, protected environments with abundant energy and surfaces for chemical reactions – for the synthesis of complex organic molecules, potentially acting as crucibles for prebiotic chemistry.

The Challenge of the Hunt

Given that impacts are a continuous process, a fundamental question arises: why have only about 30 confirmed craters been found in a country as vast as the United States? The answer lies in the formidable challenges of finding and identifying these ancient scars on a geologically active planet.

The primary obstacle is the Earth itself. Unlike the static, airless surface of the Moon, Earth’s surface is constantly being recycled. Erosion by wind, water, and ice is a relentless force that wears down crater rims and fills their basins with sediment. Over millions of years, even a large crater can be eroded to the point where no surface topography remains, leaving only the deepest structural roots and microscopic shock evidence in the rock. Tectonic activity – faulting, folding, and mountain-building – can dismember, deform, or completely destroy impact structures. Volcanic activity can bury them under thick layers of lava.

This process of erasure means that the crater record is heavily biased towards younger structures and those that formed in geologically stable regions. The ancient, stable craton of North America is one of the best places in the world to look for old craters, which is why so many have been found in the Midwest. Even there, most are buried beneath thick layers of sediment or glacial till, making them invisible from the surface.

Discovering these buried craters presents its own set of challenges. It often requires expensive geophysical surveys, such as seismic reflection or gravity mapping, which are typically conducted by the resource industry. Once a potential structure is identified, confirmation requires drilling, often to great depths, to recover rock samples for microscopic analysis. This process is costly and time-consuming. The combination of geological erasure and the difficulty of discovering buried structures means that the known craters in the United States represent only a small fraction of the total number of impacts the continent has experienced over its long history.

Watching the Skies: Planetary Defense in the 21st Century

The study of ancient impact craters is not merely a historical science; it provides the important ground truth for one of the most important forward-looking scientific endeavors of our time: planetary defense. Recognizing that the threat of a devastating impact is not just a feature of the past but a continuing reality, the United States has established a formal strategy to detect, track, and prepare for potentially hazardous near-Earth objects (NEOs).

NASA’s Planetary Defense Coordination Office (PDCO) leads this national effort. Established in 2016, its mission is to oversee all NASA-funded projects to find and characterize asteroids and comets that pass near Earth’s orbit. A key mandate, directed by Congress, is to detect at least 90% of all NEOs that are 140 meters in diameter or larger – objects big enough to cause regional devastation if they were to strike. This is accomplished through a network of ground-based and space-based survey telescopes that scan the skies nightly, cataloging new objects and refining the orbits of known ones.

Detection is only the first step. The U.S. National Planetary Defense Strategy outlines a coordinated, multi-agency approach to threat assessment and mitigation. This involves collaboration between NASA, the Federal Emergency Management Agency (FEMA), the Department of Defense, and international partners. The strategy encompasses everything from characterizing a potential impactor’s size and composition to developing emergency response plans for an impact scenario.

The ultimate goal of planetary defense is to prevent an impact from happening in the first place. To this end, NASA and its partners are developing and testing mitigation technologies. The most prominent success story is the Double Asteroid Redirection Test (DART) mission. In 2022, the DART spacecraft successfully and intentionally collided with Dimorphos, a small moonlet orbiting the asteroid Didymos. The mission was the world’s first full-scale demonstration of a kinetic impactor, proving that it is possible to alter the trajectory of an asteroid in space. Other potential mitigation techniques being studied include “gravity tractors,” which would use a spacecraft’s gravitational pull to slowly tow an asteroid off course, and, in extreme cases, the use of nuclear devices to disrupt or deflect a threatening object.

The ancient scars scattered across the American landscape serve as a stark reminder of what is at stake. By studying the geology of the Chesapeake Bay crater, scientists can better model the effects of a marine impact and the generation of mega-tsunamis. By analyzing the devastation wrought by the Barringer impactor, they can refine estimates of the airblast and ground shock from a small but dense object. The evidence of past impacts is the essential data that informs our preparations for the future, turning a story of geological history into a practical guide for ensuring human survival.

Summary

The impact craters of the United States form a diverse and scientifically invaluable collection of geological features. They are the surviving remnants of a fundamental planetary process that is largely hidden from view on our geologically active world. Each crater, whether a perfectly preserved bowl in the desert, a giant buried beneath an estuary, or a deeply eroded scar in a mountain range, offers a unique window into a moment of catastrophic change.

The formation of these craters is a process of extreme physics, where the hypervelocity collision of an asteroid or comet unleashes an explosive force that shatters, melts, and excavates the Earth’s crust in seconds. The resulting structures range from simple bowls to complex basins with central peaks and terraced walls, their final form a testament to the interplay between explosive energy and gravitational collapse. Identifying these structures requires a specialized toolkit, relying on the discovery of unique shock-metamorphic features like shatter cones and microscopic planar deformation features in minerals – the unambiguous fingerprints of a cosmic impact.

The tour of America’s craters reveals a rich history of discovery and scientific advancement. Barringer Crater in Arizona stands as the icon of impact science, the site where the impact origin of a terrestrial crater was first proven. The immense Chesapeake Bay crater demonstrates the long-lasting environmental and hydrogeological consequences of a large marine impact. The geological record in the southern U.S. preserves a vivid, ground-level view of the continent-spanning devastation caused by the Chicxulub extinction event. Craters buried deep beneath the Great Plains, such as Ames and Red Wing, have become unexpectedly valuable sources of hydrocarbons, their discovery driven by the search for energy.

These ancient scars are more than just relics of a violent past. They provide important data for understanding the history of the solar system, the potential role of impacts in the story of life, and the economic geology of our planet. Most importantly, the study of past impacts directly informs our present-day efforts in planetary defense. By understanding the consequences of events that happened millions of years ago, we are better equipped to watch the skies and develop the means to protect our future from a similar fate. The impact craters of the United States are a powerful reminder of our planet’s place in a dynamic and often violent cosmos, their stories written in stone for those who learn to read them.