Cryoseism
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A cryoseism, also known as a frost quake<ref name="wisconsin">Milwaukee Area Frostquakes. University of Wisconsin-Milwaukee (1994-02-24). Retrieved on 2006-10-22.</ref><ref name="MGS">Cryoseisms in Maine. Maine Geological Survey, the State of Maine (2005-10-06). Retrieved on 2006-10-21.</ref> or ice quake, is a non-tectonic seismic event caused by a sudden freezing action in soil or rock materials saturated with water or ice.<ref name="shortnote">Andrew V. Lacroix (January 1980). A Short Note on Cryoseisms. Earthquake Notes.</ref> As water seeps down into the rock, it freezes and expands, putting stress on surrounding rock. This builds up until it is relieved explosively in a cryoseism.<ref name="wnb">Dave Thurlow. Cryoseisms Explained. The Weather Notebook. Mount Washington Observatory. Retrieved on 2006-10-21.</ref>
Cryoseisms can also be caused by sudden glacial movements, due to the formation of a thin veneer of liquid water under a glacier from surface melting. Usually, a glacier would stick to the rough bedrock, but the hydraulic pressure acts as a lubricant, allowing it to slide several metres at once.<ref name="moment">William Orem (2004-09-14). Ice Quake!. A Moment of Science. Indiana University. Retrieved on 2006-11-16.</ref><ref>Sylvia S. Tognetti. "Climate and economic models", The Post-Normal Times, 2006-03-27. Retrieved on 2006-11-16.</ref> This type of cryoseism can last thousands of seconds long.<ref name="pdf">Tom Irvine (June 2006). Ice Quakes (.pdf). Vibrationdata Newsletter. Retrieved on 2006-11-16.</ref>
As the requirements for cryoseisms to occur are not yet defined, their prediction is still not possible. Cryoseisms constitute a significant factor in structural design and engineering.<ref name="shortnote"/> Links have been made between global warming and the frequency of cryoseisms.<ref name="pdf"/>
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[edit] Effects
Cryoseisms are often mistaken for minor or intraplate earthquakes.<ref name="shortnote"/><ref name="VGS">John E. Ebel, Richard Bedell & Alfredo Urzua (July 1995). A Report on the Seismic Vulnerability of the State of Vermont. Geology of Mineral Resources. Vermont Geological Survey. Retrieved on 2006-10-22.</ref> Although the outward signs of a cryoseism often appear similar to those of an earthquake, with tremors, vibrations, ground cracking and related noises<ref name="MGS"/> such as thundering or booming sounds,<ref name="wnb"/> cryoseisms can be distinguished from earthquakes through meteorological and geological conditions.<ref name="shortnote"/> Cryoseisms can have an intensity of up to VI on the Modified Mercalli Scale.<ref name="shortnote"/> Furthermore, cryoseisms often exhibit high intensity in a very localized area,<ref name="MGS"/> in the immediate proximity of the epicenter,<ref name="VGS"/> as compared to the widespread effects of an earthquake.<ref name="shortnote"/> The vibrations of a cryoseism are lower frequency than normal earthquakes as well.<ref name="moment"/> As a result, some seismic monitoring stations may not record a cryoseism.<ref name="VGS"/> Although cryoseisms release drastically less energy than tectonic events, and their seismic waves have stronger attenuation,<ref name="erebus">Erebus Icequakes. Mt. Erebus Volcano Observatory. Retrieved on 2006-11-16.</ref> it should be noted that cryoseisms can still cause damage or significant effects at the site.<ref name="MGS"/>
Some reports have indicated the presence of "distant flashing lights" before or during a cryoseism, possibly due to the electrical changes when the rocks are compressed.<ref name="wnb"/> Cracks and fissures can also appear, as the ground may contract and split apart from the cold.<ref name="MGS"/><ref name="VGS"/> These cracks can range from several centimetres to several kilometres long, and are usually superficial, with a single linear fracture or multiple ones as well as small vertical and moderate lateral displacement.<ref name="shortnote"/>
An ice quake prevented Walter Wellman and his team from venturing to the north pole in 1898.<ref>Arctic Postal History: The Wellman Expedition (2004). Retrieved on 2006-11-16.</ref>
[edit] Occurrences
[edit] Location
Geocryological processes have been reported to cause tremors as early as 1818.<ref name="shortnote"/> In the United States, such events have been reported in the states of Connecticut,<ref name="MGS"/> Maine,<ref name="MGS"/> Massachusetts,<ref name="MGS"/> Michigan,<ref>Prof. Kazuya Fujita (2000-10-25). Seismic Events in Michigan - Explosions and Other Events. Michigan State University. Retrieved on 2006-10-22.</ref> upstate New York,<ref name="MGS"/> Vermont<ref name="MGS"/><ref name="VGS"/> and Wisconsin,<ref name="wisconsin"/> all in the Northern and Northeastern United States.<ref name="wnb"/> Cryoseisms have also surfaced in Ontario, Canada.<ref>Frequently Asked Questions about Earthquakes. Natural Resources Canada (2006-05-08). Retrieved on 2006-10-26.</ref> Also, some glacier related phenomena have been reported in Greenland,<ref>Гренландские ледники трещат по швам (Russian). Bigli Facts. Bigli Web. Retrieved on 2006-10-22.</ref> Alaska,<ref>Alaska Glacier Tours - Know What To Look For. Alaska Channel. Retrieved on 2006-11-16.</ref> the Antarctic Prince Charles Mountains<ref>Nicole Johnston. "Surveying the Icy Peaks", Antarctic Summer, ABC News, 2002-11-29. Retrieved on 2006-11-16.</ref>and Ross Island,<ref name="erebus"/> and Iceland (Grímsvötn).<ref>The Icelandic "Icy Flood". ThinkQuest Library (October 2003). Retrieved on 2006-11-16.</ref>
[edit] Precursors
Cryoseisms typically occur when temperatures decrease from above freezing to subzero rapidly, in the first cold snap of spring.<ref name="MGS"/><ref name="VGS"/> They usually occur from midnight to dawn, during the coldest part of the night.<ref name="shortnote"/> However, glacier related cryoseisms could occur in the warmer months of summer, due to the permanent nature of glacial ice.<ref name="moment"/> Typically, cryoseisms occur 3 to 4 hours after significant changes in temperature.<ref name="precursor">D.E. Willis, R.W. Taylor, M. LeNoble, & S. Yellin (October 1979). Icequake Precursors. 51st Annual Meeting of the Eastern Section of the Seismological Society of America. Dept of Geological Sciences, University of Wisconsin-Milwaukee. Retrieved on 2006-11-16.</ref> Due to the perennial or seasonal frost conditions involved with cryoseisms, these events are limited to temperate climates which experience seasonal variation with subzero winters. Furthermore, the ground must be saturated with water, which can be caused by snowmelt, rain, sleet or flooding.<ref name="shortnote"/> Usually, the site of a cryoseism has little or no snow cover to insulate the ground.<ref name="MGS"/><ref name="shortnote"/> Geologically, an area would be most susceptible to cryoseisms if the ground is made of permeable materials like sand or gravel, which are affected by frost action.<ref name="shortnote"/> Usually, after large cryoseisms, there is no reported seismic activity for several hours, an indication that accumulated stress has been relieved.<ref name="precursor"/>
[edit] See also
[edit] References
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