Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=high&dev=">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=high&dev=">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="http://www.whoi.edu">Woods Hole Oceanographic Institute</a>)</em></small></p>Anti-crepuscular rays are beams of sunlight that appear to converge on a point opposite the sun. They are similar to crepuscular rays, but are seen opposite the sun in the sky. Anti-crepuscular rays are most frequently visible near sunrise or sunset. This photo of anti-crepuscular rays was taken at sunset in Boulder, Colorado. Crepuscular rays are usually much brighter than anti-crepuscular rays.<p><small><em> Image Courtesy of Carlye Calvin</em></small></p>An artist's rendering of the moment of impact of a massive <a href="/our_solar_system/meteors/meteors.html&edu=high&dev=">meteorite</a> at the end of the Cretaceous (at the end of the <a href="/earth/geology/hist_mesozoic.html&edu=high&dev=">Mesozoic Era</a>). Many scientists have concluded for decades that a meteorite four to six kilometers in diameter impacted the Earth at this time, resulting in a <a href="/earth/past/KTextinction.html&edu=high&dev=">mass extinction of dinosaurs</a> and many other life forms. Recent research suggests that perhaps <a href="/headline_universe/olpa/chicxulub.html&edu=high&dev=">massive volcanic eruptions</a> may be been responsible for the extinction.<p><small><em>Courtesy of Don Davis, NASA</em></small></p>March 2012 marks the first anniversary of the 9.0 magnitude <a href="/earth/geology/quake_1.html&edu=high&dev=">earthquake</a>, <a href="/earth/tsunami1.html&edu=high&dev=">tsunami</a>, and resulting nuclear accident in Japan on <a href="/headline_universe/march112011earthquaketsunami.html&edu=high&dev=">11 March 2011</a>. The tsunami did massive damage, wiping out entire villages and killing ~16,000 people, and leading to one of the most serious nuclear accidents in history. This image shows before and after photos of the area north of Sendai, where 10,000 people were lost.<p><small><em>Photos by <a href="http://www.nytimes.com/interactive/2011/03/13/world/asia/satellite-photos-japan-before-and-after-tsunami.html?hp">GeoEye/EyeQ</a>.</em></small></p>An <a href="http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc000905e.php">8.6 magnitude earthquake</a> struck on 11 April 2012 off of Banda Aceh, Sumatra, Indonesia, followed by a strong aftershock. Earthquake motion was primarily horizontal. A tsunami warning was issued for the Indian Ocean, but was cancelled at 12:36 UTC. A tsunami was observed at 1 meter or less. Find out more about <a href="/earth/geology/quake_1.html&edu=high&dev=">earthquake</a> and <a href="/earth/tsunami1.html&edu=high&dev=">tsunami</a> processes. Check out the resources <a href="/teacher_resources/2011_AGU-NESTA_GIFT_Workshop.html&edu=high&dev=">here</a>.<p><small><em>NOAA</em></small></p><p>Something on Earth is always burning! NASA's Earth Observatory tracks wildfires across the world with <a href="http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD14A1_M_FIRE" target="_blank">maps available for viewing</a> from 2000-present. Some wildfires can restore <a href="/earth/ecosystems.html&edu=high&dev=">ecosystems</a> to good health, but many can threaten human populations, posing a natural disaster threat.</p> <p>Check out the materials about natural disasters in <a href="/earth/natural_hazards/when_nature_strikes.html&edu=high&dev=">NBC Learn Videos</a>, and their earth system science connections built up by the related secondary classroom activities.</p><p><small><em>NBC Learn</em></small></p>


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