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Astronomy/Craters
[[Image:Chain of impact craters on Ganymede.jpg|thumb|right|250px|The image shows a chain of craters on Ganymede. Credit: Galileo Project, Brown University, JPL, NASA.]]
A '''crater''' may be any large, roughly circular, depression or hole in or beneath the rocky surface of a rocky object.

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'''Secondary craters''' are impact craters formed by the ejecta that was thrown out of a larger crater. They sometimes form radial crater chains.

"The present paper deals with the problem of estimating the flux of objects large enough to produce impact craters on earth."<ref name=Shoemaker>{{ cite journal
|author=E. M. Shoemaker
|title=Astronomically observable crater-forming projectiles, In: 
''Impact and Explosion Cratering: Planetary and terrestrial implications''
|publisher=Pergamon Press, Inc.
|location=New York
|month=
|year=1977
|volume=
|issue=
|pages=617-28
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A '''caldera''' is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters. The word comes from Spanish ''caldera'', and this from Latin <small>CALDARIA</small>, meaning "cooking pot". In some texts the English term ''cauldron'' is also used.

About 75,000 years ago, this Indonesian volcano released about 2,800
 </sup> km<sup>3</sup> DRE of ejecta, the largest known eruption within the Quaternary Period (last 1.8&nbsp;million years) and the largest known explosive eruption within the last 25&nbsp;million years. In the late 1990s, anthropologist Stanley Ambrose<ref name=Ambrose>[http://www.anthro.illinois.edu/people/ambrose Stanley Ambrose page at University of Illinois at Urbana-Champaign]</ref> proposed that a volcanic winter induced by this eruption reduced the human population to about (contracted; show full)[[Category:Astrophysics/Lectures]]
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