An impact in the Andes
About 663,000 years ago, a metallic asteroid roughly 15 meters in diameter plunged through the thin, high-altitude atmosphere of the Andes mountains. It struck the ground at approximately 15 kilometers per second, hitting an area of Paleozoic granite and Pliocene ignimbrite (a type of volcanic rock) at an elevation of 3,015 meters. The impact released energy comparable to multiple nuclear bombs, heating the ground to temperatures between 1,500 and 1,600°C.
This intense heat instantly melted the granite, creating a unique type of rock known as impactite, or impact glass. The event excavated a bowl-shaped crater measuring about 350 by 370 meters across and 34 meters deep. The resulting structure is one of the best-preserved small impact craters on Earth, a status is due to its location in the Atacama Desert, one of the driest environments on the planet. The crater was first identified from aerial images in 1962 and confirmed as an impact structure in 1966.
Geological history
The material ejected from the crater, including the newly formed impact glass, is found primarily on the southern and southeastern sides of the rim. This distribution suggests the asteroid came in at an angle, striking from the northwest. The impact glass itself is a composite material. It contains a heterogeneous glassy matrix mixed with fragments of shocked and unshocked granite, quartz, and feldspar.
Embedded within this glass are tiny metallic spherules of nickel and iron—the remains of the vaporized IAB iron meteorite. These spherules make some pieces of the impactite magnetic. The glass also contains high-pressure minerals like coesite, a form of quartz created under extreme pressure. The arid conditions of the Atacama have prevented significant erosion, preserving these fragile geological signatures for hundreds of thousands of years. This helps scientists study the physics of small impact events in a detail that is rarely possible elsewhere.