The critical zone

1
The critical zone
The Critical Zone includes the land surface and
its canopy of vegetation, rivers, lakes, and
shallow seas, and it extends through the
pedosphere, unsaturated vadose zone, and
saturated groundwater zone. Interactions at this
interface between the solid Earth and its fluid
envelopes determine the availability of nearly
every life-sustaining resource.
http//www.nap.edu/catalog/9981.html
2
The four Grand Challenges facing Critical Zone
Science
http//www.czen.org/files/CZEN_paper.pdf
3
The critical zone

• At Earths surface, a complex suite of chemical,
  biological, and physical processes combines to
  produce soil from bedrock and sediments within
  the zone that extends from the outer limits of
  vegetation to the lower limits of groundwater.
  This weathering engine transforms primary
  minerals, provides nutrients to nourish
  ecosystems and human society, mediates the
  transport of toxic components within the
  biosphere, creates water flow paths that shape
  and weaken bedrock, and contributes to the
  evolution of landscapes at all temporal and
  spatial scales. At the longest time scales, the
  weathering engine sequesters CO2, thereby
  influencing the global carbon cycle, long-term
  climate change, and weathering rates.
• --http//www.czen.org

4
Weathering

• Geomorphic processes operate on surficial
  materials not just bedrock
• Definition  Weathering is the disintegration and
  decomposition of rocks and minerals at or near
  the earth's surface as a result of physical,
  chemical, and biological processes.  No transport
  or entrainment is considered.
• Surficial materials     Bedrock     new
  materials created by weathering     resistant
  materials     organic debris
• We divide weathering into two principal process
  types, although they do not work independently
• Physical (or mechanical) weathering
  -disaggregation with no change in chemistry 
  creates surface area
• Chemical weathering -alteration to cause
  chemical or mineralogic changes  weakens rocks
• Primary controls on weathering  climate
  (temperature and precipitation) and geology (rock
  type and distribution).
• Secondary controls  topography (relief and
  aspect) and vegetation (changes chemistry and is
  vigorous physically).

5
Environmental control on weathering
6
(No Transcript)