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sinkhole |
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sinkholeor sink or dolineDepression formed as underlying limestone bedrock is dissolved by groundwater. Sinkholes vary greatly in area and depth and may be very large. The two main varieties are those caused by the collapse of a cavern roof, and those caused by the gradual dissolving of rock under a soil mantle. Collapsed sinkholes generally have steep rock sides and may receive streams that then flow underground. Soil-mantled sinkholes are generally shallower; they may become clogged with clay and hold a small lake. sinkhole [′siŋk‚hōl] (geology) Closed surface depressions in regions of karst topography produced by solution of surface limestone or the collapse of cavern roofs. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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Based on the experiences of a teacher who worked with inmates at San Quentin State Prison, the site features earth-science lessons and activities such as mapping the schoolyard, identifying rocks and learning about sinkholes. In the Arctic, land that was once permanently frozen is collapsing into giant sinkholes. Such paid and unlabeled government propaganda is actually common, especially in such tax sinkholes as the Office of National Drug Control Policy, which has spent $1 billion since 1998 on both direct and unlabeled anti-drug promotions in advertising and TV shows. |
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