Transcript Solution and Precipitation

McKnight's
Physical Geography
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.
Often
in limestone
– calcium/carbonate
rocks
Caverns
anddeposits
Related
Features
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”
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
Isolated “tower karsts”
after caves wash away
[Insert Fig. 17-7 p. 412]
• Sinkholes
Karst Topography
– 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
Fumaroles
Hydrothermal
Features
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–
–
–
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
Hydrothermal features
in Yellowstone
Features
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–
–
–
–
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