GEOG 1350 Chapter Notes - Chapter 8: Karst, Frost Heaving, Sinkhole

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16 Aug 2016
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GEOG1350 Katy Lemaire
October 14th, 2015.
CHAPTER 8- SUBSIDENCEE AND SOIL EXPANSION AND CONTRACTION
8.1 Introduction
subsidence is a slow or rapid, nearly vertical, downward movement of Earth’s surface
subsiding areas can be circular, linear, bead like or irregular. It can involve imperceptible
lowering of the land surface over a large area.
-commonly associated with dissolution of limestone, dolostone, marble, gypsum or rock
salt at depth, resultant karst landscape is irregular in form of closed depressions
-causes can include thawing of frozen ground, compaction of recently deposited
sediment, shrinkage of expansive soils, earthquakes or deflations of magma chambers
-its important to note that soil is defined as a mixture of unconsolidated mineral and
organic material at Earth’s surface that has been modified by physical, chemical and
biological weathering processes
Karst
-results from dissolution and subsidence of near surface rocks
-water+ carbon dioxide= carbonic acid
Sinkholes: large openings close to the surface, first type is solution sinkholes in which
the pits form by a solution of bedrock in holes that develop along bedding planes, joints
and fractures. Collapse sink holes develop by a collapse in the surface rock or sediment
into an underground cavern system.
Cave Systems: as solution pits in limestone enlarge, a system of caves form, caves
develop at or near groundwater table where water that is saturated with calcium and
bicarbonate is replaced with water that is not saturated, if the ground water table falls
seeping water will deposit calcium carbonate on sides, floors and ceiling of the cave.
Tower Karst: large steep limestone pillars that rise above the surrounding landscape,
residual land forms of a highly eroded karst landscape
Disappearing Streams: surface streams that disappear and are carried into caves
Springs: natural discharge of water at the ground surface, have heavy flows but are
generally drying up now
Permafrost
-permanently frozen ground with sediment remaining frozen for at least 2 years
-Canada is underlain by permafrost
-typically exists in any climate where the mean annual air temperature is below zero
degrees Celsius
-some sediments can expand when they freeze
-frost susceptible sediments expand when they freeze due to the 9% increase in volume
that occurs when water changes to ice, which increases the cause of an upward
movement of sediment particles and the land surface which is known as frost heaving
Piping: groundwater slowly percolates through loose sediments it can pick up particles
of silt and sand and carry them laterally to a point of water discharge on a slope, over
time, shallow subterranean tunnels may develop in sediments and collapse to produce
surface depressions.
Sediment Compaction: (a) Fine: clay, silt and sand contain an abundance of pore
water which is water occupying the spaces among the particles that constitute the
sediment. Rapid deposition and compaction are common. (b) Collapsible: large pore
space and grains that are loosely bound or water soluble, may remain dry long after
they form, large amounts of infiltrating water will weaken the bonds and dissolve the
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