(MODULE 6) WEATHERING & SOIL FORMATION Flashcards
the physical breakdown and chemical alteration of rock
weathering
the physical removal of rock particles by mobile agents (water, wind, ice, gravity)
erosion
movement of eroded particles by agents (rivers, waves, glaciers, wind)
transportation
weathering which breaks up rock but doesn’t change composition
mechanical weathering
decomposition of rock from exposure to water and atmospheric gases; as rock is decomposed by these agents, new chemical compounds form
chemical weathering
reduction of pressure on a body of rock; can cause rock to crack as it expands
pressure release
how does pressure release happen and how do sheet joints form?
the pressure on top of the deep pluton is released through unloading, causing an uplift on the plutonic rock which expands and develops cracks called sheet joints which develop parallel to the outer surface of the rock.
why can’t sheet joints exist without clay?
the sheet joints contain cleavage surfaces between the slabs, hence the name. when the sheet joints form, they become weak surfaces which flake off.
on slopes, gravity may cause the rock between the joints to break loose in concentric slabs from the underlying granite mass. this process of spalling off of rock layers is called ___.
exfoliation
the mechanical effect of freezing water on rocks
frost action
the expansion of freezing water pushes rock apart
frost wedging
the expansion of freezing water pushes rock apart
frost wedging
vertical expansion of rock and soil due to water freezing underneath the surface
frost heaving
particularly roots growing in cracks can break up rocks
plant growth
___ can cause a rock to expand until it breaks.
extreme changes in temperature
mechanical weathering can ___, accelerating the rate of chemical weathering
increase the surface area of a rock
the decomposition of rock from exposure to water at atmospheric gases
chemical weathering
chemical weathering changes the ___ of rocks
composition
chemical weathering is a ___ process, as the mineralogy of the rock adjusts to the near surface environment
gradual and ongoing
chemical weathering is ___ such as the presence of water and oxygen
enhanced by geological agents
major processes of chemical weathering:
1.
2.
3.
- dissolution
- oxidation
- hydrolysis
major processes of mechanical weathering
1.
2.
3.
4.
- pressure release
- frost action
- plant growth
- extreme temperature change
aided by small amounts of acid in the water
dissolution
the most important natural source of acid for rock weathering at earth’s surface is ___ in water.
carbon dioxide
water and carbon dioxide form ___, the acid featured in dissolution.
carbonic acid
the decomposition of rock through dissolution is ___.
gradual and subtle
___ are processed because they are acidic and cause changes in the surroundings; they originate from mines and its draining processes
mine tailings
any reaction when electrons are lost form one element
oxidation
oxygen from the atmosphere combines with the iron to form iron oxide. iron oxide formed through oxidation is a weathering product of numerous minerals containing iron, such as the ___ group.
ferromagnesian
___ is a good indication of oxidation.
color
resulting mineral when oxygen combines with iron to form iron oxide through oxidation.
hematite
the reaction of any substance with water
hydrolysis
how does hydrolysis occur?
hydrogen ions destroy the arrangement of the rocks’ atoms and create new minerals in its place
factors affecting weathering
1.
2.
3.
4.
- availability of water
- climate
- temperature
- steep slopes, precipitation, freezing/thawing, flowing glacial ice
rock chemically weathers much faster in ___ than in arid climates.
humid climates
the most intense chemical weathering occurs in ___.
the tropics
a natural process; it is part of the constant recycling of earth materials that we call the rock cycle
soil erosion
types of soil erosion
1.
2.
- splash erosion
- sheet erosion
splash erosion requires ___, whereas sheet erosion requires ___.
- water
- movement of sediments
the rate of soil erosion is influenced by several factors:
1.
2.
3.
4.
- soil characteristics
- climate
- slope
- vegetation
course-grained soils tend to have ___ and can ___ than fine-grained soils (clay)
- larger pore spaces
- absorb more water
a gentle rain over a long period of time produces ___ than a short, heavy rain storm.
less splash erosion
___ can infiltrate the soil during gentle rainfall and there is ___ of sheet erosion occurring.
- more water
- less likelihood
water moves more slowly on ___ and is more likely to percolate down into the soil.
gentle slopes
the faster-moving water on ___ does not infiltrate and has greater ability to dislodge and transport soil particles down from the slope.
steeper slopes
