1. 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.

2. 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

3. 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

4. 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.

5. 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”

6. 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 p. 412]
Isolated “tower karsts” after caves wash away

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

8. Extent of karst topography

9. 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

10. 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

11. 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

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

13. 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?>

14. 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