A ladder 9.00m long leans against the side of a building. If the ladder is inclined at an angle of 75.0 to the horizontal, what is the horizontal distance from the bottom of the ladder to the building?
GEOL 110 Ch8 323 Karst, cont. •Sinkholes –Vary in size from one to several hundred meters in diameter –Can open up extremely rapidly •Two Basic types –Solutional sinkholes •Acidic groundwater becomes concentrated in holes in joints and fractures in the rock •Water is drawn into a cone above the hole in the limestone –Collapse sinkholes •Develop by the collapse of material into an underground cavern •Cave systems –Formed when dissolution produces a series of caves –Related to fluctuating groundwater table –Groundwater seepage causes flowstone, stalagmites, stalactites Some caves can also contain crystals forming from waterreach ions Karst, Cont. Characteristics of Karst Topography •Tower Karst –Large, steep limestone “towers” –Created in highly eroded karst regions •Disappearing Streams –Streams that suddenly disappear into cave openings –Actually flow directly into the groundwater system •Springs –Places where groundwater naturally discharges at the surface Thermokarst •In polar or high altitude regions, permafrost exists –Sediment remains frozen throughout the year –Soil or sediment cemented with ice for at least 2 years •When permafrost thaws it can create land subsidence within the land •Extensive thawing creates uneven soil called thermokarst Sediment and Soil Compaction •Fine sediment –Sediment collapses when water is removed –Common on river deltas –Flooding replenishes sediment, thwarting collapse •Collapsible soils –Dust deposits, loess, and stream deposits in arid regions are bound with clay or water soluble minerals –Water weakens bonds causing soil to collapse •Organic soils –Wetland soils contain large amounts of organic matter and water –When water drained or soil is decomposed, soils collapse Earthquakes •In subduction boundaries, when fault is locked, land can become uplifted •After an earthquake, the land subsides Underground Drainage of Magma •Magma –Uplifts the land during an eruption –Afterwards land subsides •Lava tubes –Form when molten lava drains out from underneath cooled surface lava –Leaves void near the surface that is susceptible to collapse Expansive Tools •Expand during wet periods and shrink during dry periods –Common in clay, shale, and clayrich soil containing smectite –After expansion, soils can have cracks and popcornlike texture •Often will produce wavy bumps in surfaces –Causing tilting and cracking of sidewalks, foundations, utility poles, and headstones Geographic Regions at risk for Subsidence and Soil Volume Change •Karst topography composes about 10 percent of Earth’s surface –About 25 percent of United States •Region through Tennessee, Virginia, Maryland, and Pennsylvania •Southcentral Indiana and westcentral Kentucky •SalemSpringfield plateaus of Missouri and northernmost Arkansas •Edwards Plateau of central Texas •Most of central Florida •Puerto Rico •Permafrost covers more than 20 percent of world’s land surface –Most of Alaska and more than half of Canada and Russia Cont. •Compaction of sediment –World’s marine deltas •Organicrich clays in coldregion wetlands –New England –Washington State –Alaska •Coastal wetlands –Florida Everglades –SacramentoSan Joaquin Delta in California –Costal Louisiana and North Carolina •Expansive soils –Western United States and Canada –Swelling clays found in all 50 states •Frost heaving –Alaska –Northern contiguous United States and Canada •Seismicrelated –Alaska –Hawaii –Pacific Northwest Effects of Subsidence and Soil Volume Change •Karst formation and soil expansion and contraction cause significant economic damage each year •Problems include –Sinkhole formation –Changes in groundwater conditions –Damage caused by melting permafrost –Coastal flooding and loss of wetlands –Damage caused by soil volume change 8.7 Human Interaction with Subsidence and Soil Volume Change •Humans can contribute to problems associated with subsidence and soil volume change –Withdrawal subsurface fluids –Excavate underground mines –Thawing frozen ground –Restriction of deltaic sedimentation –Alter surface drainage –Use poor landscaping practices