L9: Weathering Flashcards
What is mechanical weathering?
- The physical break-up of rocks without changes in the rocks composition
- Have many causes, ex.:
- Rocks having zones of weakness along which they break
- Temps. Fluctuate above and below freezing so water in the cracks repeatedly expand and freeze, forcing the rocks apart
What is exfoliation?
A process in which large sheets of rock are detached from the outcrop
What is frost wedging?
Occurs from the expansion of freezing water which exerts an outward force sufficient enough to wedge open a pre-existing crack and split the rock
What is the principle effect of mechanical weathering?
The break up of large chunks of rock into smaller ones and therefore increasing
What is chemical weathering
- Involves the breakdown of minerals by chemical reaction with water or gases in either the atmosphere/pore-waters
- Dependent on the rock composition and the climate we’re in
- Least stable = weathers faster
- More stable = weathers slower
The more ________ you have, the greater the weathering will be. What is the impact of this?
- Surface area
- Smaller pieces will weather fast bc greater surface area
What are the 2 most important factors related to chemical weathering?
- Parent material
- Climate
Describe parent material
- Minerals differ in the kinds of chemical reactions they undergo
- High temperature formed minerals are least stable at surface, oxygenated conditions
- Whereas secondary minerals are most-stable
Describe climate in regards to chemical weathering
- Climate plays a major role in the intensity of chemical weathering
- Chemical reactions require water; the more water = the more intense the chemical weathering
- Most chemical reactions proceed more rapidly at high temperatures than colder temperatures
- Also dictated by compositional material and climate
How is clay formed?
From the weathering or preexisting minerals
What are the 2 types of biological weathering
Mechanical
Chemical
What is biological weathering?
break that shit down biologically
Mechanical weathering
- Action of tree roots in splitting the rock apart
- Roots pull into rock and increase SA
Chemical weathering
Organic acids are produced through decaying vegetation (ex. Carbonic acid)
What forms soil?
Biomass weathering
Define erosion
The action of surface processes that removes soil, rock, or dissolved materials from one location on earth’s surface and then transport it to another
What are the 4 methods of transportation?
- Gravity
- Water
- Ice
- Wind
Gravity
- Typically the material that accumulates at the bottom of landslides collectively known as “colluvium”
- Material travels to the bottom
- Aids in forming soil
Water
Have deposits known as alluvium (ricer; stuff that rivers transport), lacustrine (lake), marine (oceans)
Ice
- As glacial ice advances, the underlying soils and rock are removed and eroded
- As ice melts and glacier retreats, the glacial degree/drift remains and provides a new source of material for soil formation
- Highest energy
Wind
- AKA Eolian Deposits
- Formed via the accumulation of wind blown dust
- When they’re deprived of glacial material, composed primarily of silt and clay
What are the most important stream deposits? Why?
- Floodplains
- They’re fertile because weathered stuff in a river continues to be carried by the river
- Acts as a source of settlement because because the land is fertile because material is transported from one place to another
Weathering = mechanism that __________. Erosion = mechanism that _________
- Breaks rocks apart
- Moves rocks from one place to another
50% of soil = ________. 90% of that = __________
- Solid matter
- Inorganic material
What is a soil profile
Vertical sequence of horizons
What are soil horizons?
Organization of soil properties into layers that change vertically in depth
What types of soils end up with layers?
Homogeneous soils
What leads to soil formation?
All 3 weathering processes and erosion
What zone has the most accumulation?
The D layer
