mcknight's physical geography chapter 17 karst and hydrothermal processes modified by aj allred...
TRANSCRIPT
McKnight's Physical Geography
Chapter 17
Karst and HydrothermalProcesses
Modified by AJ Allred
for SLCC Fall 2013
© 2014 Pearson Education, Inc.
Andrew MercerMississippi State University
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 acidcarbonic acid– Most effective on carbonate sedimentary rocks (e.g.,
limestone)
– Calcium carbonate reaction• CaCO3 + HH22O + COO + CO22 = 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 sulfuricsulfuric 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 FeaturesOften in limestone deposits – calcium/carbonate rocks
Five stages1. Initial excavation – water finds a way in
2. Decoration stage – mild acid erosion caves
3. Dissolved solution precipitates back into “drip-dry” rockspeleothems form (stalactites and stalagmites)
4. Structural collapse - caves eventually “cave in”
5.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 TopographyExtent 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 FeaturesFumaroles– 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 FeaturesHydrothermal 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