METEORITE IMPACT AND AIRBURSTS AS A NATURAL HAZARD (Invited Presentation)

Impacts of extraterrestrial bodies are among the most spectacular, high-energy geological processes on Earth. Of particular interest are the effects and dangers of typical impact events for the geological and biological evolution of the Earth. For example, a huge impact, 65 million years ago, marking the end of the Cretaceous, had a catastrophic influence on the biosphere. Astronomical studies of minor planet orbits, as well as dating of known impact craters, allow deriving the frequency with which impact of certain sizes occur on Earth. Bodies with a diameter of 1-2 km, which would cause craters on the order of 20-40 km in diameter (such as the Ries Crater in southern Germany), hit the Earth on average about once every million years. Smaller impacts, leading to craters of about 1 km in diameter (e.g., Meteor Crater in Arizona, USA), occur much more often, namely every few thousand years. Really large impacts, which cause craters with diameters of more than 100 km, are fortunately not as common and happen only every 50-100 million years. But such large impacts cause global catastrophes and can even lead to mass extinctions of life on Earth. However, the explosion of small bodies in the atmosphere probably constitute the most severe danger to humankind. In 1908, a stony meteorite probably about 50 m in diameter exploded about 10 km above the Siberian Taiga, destroying about 2000 sq km of woods. This is an area much larger than, e.g., Washington, Manhattan, Berlin, or Vienna. In 2013, a much smaller body, about 20 m in diameter, exploded near the Russian city of Chelyabinsk, at an altitude of about 25 km, and about 65 km from the city. This explosion carried an energy of about 30 times that of the Hiroshima atomic bomb. Such airbursts are quite common and, if they would happen over occupied areas, could cause thousands to hundreds of thousands of deaths. Meteorite impact and airbursts need to be taken serious as natural hazards.