reporters: allen june buenavista jambee bernales
DESCRIPTION
KARST. Reporters: Allen June Buenavista Jambee Bernales. KARST PROCESSES & LANDFORMS Karst connotes an assemblage of landforms and the dissolution of a layer or layers of soluble bedrock most common in carbonate rocks (limestone, dolomite) also occurs in evaporites (salts) - PowerPoint PPT PresentationTRANSCRIPT
Reporters:
Allen June Buenavista
Jambee Bernales
KARST PROCESSES & LANDFORMS
Karst connotes an assemblage of landforms and the dissolution of a layer or layers of soluble bedrock
most common in carbonate rocks (limestone, dolomite)
also occurs in evaporites (salts) also occurs on ice
B. Driving Forces
SolutionMain reaction: CaCO3 + H2O + CO2 = Ca+2 + 2HCO3
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Factors controlling the solution rate amount dissolved CO2
partial pressure of CO2 in air: PCO2 increases, the quantity of CO2 absorbed by water increases
temperature: cooler water is capable of dissolving more CO2 than warmer water at a given PCO2
biological processes: decaying humus is an important source of CO2
climate temperature, precipitation, biological
activityrunoff generation is the most important
effect of climate
C. Resisting Framework
Lithology and structure
ideal conditions for a fully developed karst landscape requires limestone that is:fairly pure; over 60% calcite for some
karst; over 90% calcite for fully developed karst landscape
very thickmechanically strongmassively jointed
POROSITY AND PERMEABILITY
porosity: percentage of pore spaces in a given volume of rock or soil
primary porosity - intergranular voids; affected by:grain size distributionparticle shapedegree of packing
secondary porosity: voids due to joints, faults, fractures or bedding planespromotes circulation by increasing
permeability
porosity is important only if rocks are also permeable
permeability: ease with which rock or soil transmits water
E. Karst Landforms -Dolines (Sinkholes)
•SOLUTION sinkholes
Image: Tihansky (1999) USGS Circular 1182
Map and Image
SUBSIDENCE sinkholes
Image: Tihansky (1999) USGS Circular 1182
• COLLAPSE sinkholes
Image: Tihansky (1999) USGS Circular 1182
Chocolate Hills, Bohol
Requirements:
-Thick and extensive mass of limestones/dolostone
-underlying impermeable stratum-surface layer of impermeable rock for the
initiation of stream pattern.
Youth Stage- upper impermeable stream is removed by the streams, which then proceeds to disappear underground through enlarged joints and fractures.
Through the youth stage the underground drainage develops slowly and when drainage is all underground MATURITY is reached.
LATE MATURITY- the underground stream reach impermeable underlying stratum and the collapse of the cavern roofs due to lowering of the surface
OLD AGE- all roofs disappear and the drainage reappears at the surface on the exposed impermeable bed.
Karst towers and hills
•A poor understanding of Karst terrain has led to land-use practices that pose significant economic and environmental impacts to households and communities.
•Sinkhole collapse, either slow or dramatic, regularly causes considerable damage to buildings, highways, rails, bridges, pipelines, storm drains, and sewers. •
sinkholes provide a pathway for surface water to directly enter groundwater aquifers, so the potential for pollution is high because of the minimal filtering of surface water.(permeability of limestone, dolostone, etc.)
Sinkhole formation is closely related to local hydrologic conditions, and human-induced changes to the local hydrology commonly accelerate the process.
Diverting surface water, pumping groundwater,
and constructing reservoirs all contribute to sinkhole collapse.
The most notable incidents occurred in the City of Staunton: on August 11, 1911, parts of several homes and the firehouse were lost in a series of sinkholes on Baldwin Street and Central Avenue, and on October 28, 2001, a 45-feet deep chasm opened up on Lewis Street.
Sinkholes regularly cause problems along roads and highways in the Commonwealth. During the past thirty years, VDOT’s Staunton District has recorded 350 sinkholes that have damaged roads throughout the district.
Signs of sinkhole formation:Slumping or falling fence postsWilting(bend) vegetation Discolored well waterStructural cracks in walls, floors, or foundations.