reporters: allen june buenavista jambee bernales

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.