McKnight's Physical Geography Karst and Hydrothermal Processes Chapter 17 Karst and Hydrothermal Processes Modified by AJ Allred for SLCC Fall 2013 Andrew Mercer Mississippi State University © 2014 Pearson Education, Inc.

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

Solution and Precipitation Dissolution – carbonic acid Most effective on carbonate sedimentary rocks (e.g., 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 and acids from nitrogen oxides

Solution and Precipitation 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 present in hot springs. Hot water has more minerals, except carbon dioxide.

Caverns and Related Features Often in limestone deposits – calcium/carbonate rocks Five stages 1. Initial excavation – water finds a way in 2. Decoration stage – mild acid erosion caves 3. Dissolved solution precipitates back into “drip-dry” rock speleothems form (stalactites and stalagmites) 4. Structural collapse - caves eventually “cave in” Eventually, most of the formation washes away, leaving isolated “tower karsts”

Karst Topography Mild acid easily dissolves hard limestone Typical landforms Sinkholes Disrupted surface drainage Ten percent of Earth’s land surface – soluble rock [Insert Fig. 17-7 p. 412] Isolated “tower karsts” after caves wash away

Karst Topography Sinkholes Rounded depressions – sinking areas Collapse dolines Disappearing streams Karst Topography

Extent of karst topography

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

Hydrothermal Features 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

Hydrothermal Features Fumaroles Surface crack connected to a deep-seated heat source Little water drainage Water that is drained – converted to steam Steam vent, either continuously or sporadically

Natural travertine layering – often used for building decoration Soda Springs, Idaho. This deposition is provided by a 100 foot geyser that erupts every hour.

Hydrothermal Features 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 Many geothermal features seem weaker than in past decades. What might global warming have to do with it? <DROUGHT?>

Hydrothermal Features Hydrothermal features in Yellowstone 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