Ch17

Chapter 17: Karst and Hydrothermal Processes

McKnight’s Physical Geography: A Landscape Appreciation,

Tenth Edition, Hess

Karst and Hydrothermal Processes

• The Impact of Solution Processes on the Landscape

• Solution and Precipitation• Caverns and Related Features• Karst Topography• Hydrothermal Features

2© 2011 Pearson Education, Inc.

The Impact of Solution Processes on the Landscape

• Mechanical effects of underground water have limited topographic influence

• Water’s solvent properties allow it to dissolve certain chemicals from rock

• Hydrothermal vents


Solution and Precipitation

• Water in its pure form is a poor solvent

• Chemical impurities make water a good solvent of a few underground minerals

• Carbonic acid


Figure 17-1


• Dissolution– Most effective on carbonate sedimentary rocks (i.e.,

limestone)– Calcium carbonate reaction

• CaCO3 + H2O + CO2 = Ca(HCO3)2

– Dolomite reaction• CaMg(CO3)2 + 2H2O + 2CO2 = Ca(HCO3)2 + Mg(HCO3)2

– These are most notable dissolution processes– Occurs more rapidly in humid regions– Possible role of sulfuric acid



• Role of bedrock structure– Profusion of joints allows for

groundwater penetration• Precipitation processes

– Mineralized water trickles along cavern roof or wall

– Reduced air pressure precipitates mineral material

– High mineral content in hot springs


Figure 17-2

Caverns and Related Features

• Large openings beneath the Earth’s surface that result from solution processes

• Often found in areas with massive limestone deposits

• Two principal stages– Initial excavation– Decoration stage:

speleothems– Stalactites and stalagmites

7© 2011 Pearson Education, Inc.Figure 17-3

Karst Topography

• Topography that results from underground dissolution

• Typical landforms– Sinkholes– Disrupted surface

drainage– Underground drainage

networks• Ten percent of land surface

is soluble rock


Figure 17-5

Karst Topography

• Sinkholes– Rounded depressions that

form from dissolution of surface carbonate rocks

– Collapse dolines– Wide range of sizes– Fundamental karst unit of

erosion and weathering– Chains of sinkholes: uvala– Tower karst– Disappearing streams and

swallow holes


Figure 17-9

Karst Topography

• Extent of karst topography

10© 2011 Pearson Education, Inc.Figure 17-6

Hydrothermal Features

• Hydrothermal activity– Geysers and hot springs

• Hot springs– Water heated by magma– Forced upward from

pressure resulting from heating

– Resulting topography from hot springs

– Algae growth


Figure 17-10


• Geysers– Intermittent hot spring– Accumulation of

superheated water and steam builds pressure

– Tremendous heat required for geyser formation

– Variable eruption times– Variable deposits, most are

sheets of deposits scattered irregularly over ground


Figure 17-12


• Fumaroles– Surface crack connected to

a deep-seated heat source– Little water drainage– Water that is drained is

converted to steam– Steam issuing vent, either

continuously or sporadically


Figure 17-14


• Hydrothermal features in Yellowstone – 225 geysers– Volcanic bedrock materials– Shallow magma chamber,

mantle plume (heat source)– Copious summer rain and

winter snowmelt (water source)

– Numerous fractures and weak zones from earthquakes


Figure 17-13


• Hydrothermal features in Yellowstone (cont.)– Geyser basins in same

watershed on west side of park

– Geyser basins drained by three rivers

– Geyser basins have extensive geyserite

– Mammoth Hot Springs Terraces


Figure 17-16

Summary

• Solution processes are important to the underground landscape

• Solution processes can also result in hydrothermal features and karst topography

• Two major soluble rocks, calcium carbonate and dolomite, are involved in most dissolution processes

• Joints and fractures in the bedrock allow for greater water percolation and greater dissolution

• Minerals which fall out of solutions that are trickling along cavern walls or ceilings are called precipitation


Summary

• Numerous cavern features result from solution processes, which are referred to as speleothems

• Stalactites and stalagmites are common features within caverns

• Modification of the land surface by subterranean solution processes results in karst topography

• The most common karst landforms are sinkholes• Hydrothermal features exist in areas where hot water

moves to the Earth’s surface through openings


Summary

• Hot springs are bubbling basins of hot water that are heated naturally

• Geysers result from an area of superheated water that builds up pressure until the water erupts from an opening

• Fumaroles occur when small amounts of water are introduced into a hydrothermal vent

• Yellowstone contains the largest percentage of hydrothermal features in the world


Technology

Ch17