Weathering ang Erosion Flashcards
is the decomposition
and disintegration of rocks and
minerals at the Earth’s surface.
It involves little or no
movement of rocks and minerals – the weathered material accumulates
where it forms and overlies
unweathered bedrock.
Weathering
is the removal of weathered
rocks and minerals by moving water,
wind, glaciers, and gravity. After a
rock fragment has been eroded from
its place of origin, it may be
transported large distances by the
agents mentioned above.
Erosion
When the wind or water loses energy,
or when the ice carrying the
weathered material melts, transport
stops, and sediment is _________
deposited
wetlands that form as rivers
empty their water and sediment into
another body of water
delta
reduces solid rock to rubble but does not alter the chemical composition of rocks and minerals.
Mechanical weathering
occurs when air and water chemically react with rock to alter its composition and mineral content.
Chemical weathering
Five major processes of Mechanical Weathering
- Pressure-release fracturing
- Frost wedging
- Abrasion
- Organic activity
- Thermal expansion and contraction
as pressure diminishes, rock expands – which leads to fracturing of brittle rock.
major processes of Mechanical Weathering
Pressure-release fracturing
water expands when it freezes. If water accumulates in a crack then freezes, its expansion pushes the rock apart
major processes of Mechanical Weathering
Frost wedging
mechanical weathering and grinding of rock surfaces by friction and impact.
major processes of Mechanical Weathering
Abrasion
roots may work their way down into cracks in the
rock, expand, and eventually push the rock apart.
major processes of Mechanical Weathering
Organic activity
rocks are exposed to daily and yearly cycles of heating and cooling , which, as a result, the surface expands or contracts faster than the interior
major processes of Mechanical Weathering
Thermal expansion and contraction
Chemical Weathering
Three most important processes:
- Dissolution
- Hydrolysis
- Oxidation
rocks are made up of minerals, and minerals are
chemicals on their own. To understand how acids and bases dissolve minerals , think of an atom on the surface of a crystal, which could be dissolved when subjected to the certain solvents.
Chemical Weathering
Dissolution
water reacts with a mineral to form a new mineral with the water incorporated into its crystal structure.
Chemical Weathering
Hydrolysis
many minerals react with atmospheric oxygen , O2 Rusting is one example of a more general process called __________
Chemical Weathering
Oxidation
Significance of Weathering
most important aspect of weathering is its role in the formation of soil.
Weathering is important to engineers because it can help them to understand **how buildings and other structures will be affected by the environment. **
Weathering is also important to geologists because it can help them to study the history of the earth’s surface.
The Effects of Weathering (3)
- weakening of intact rock blocks and soil grains
- integral become mechanical discontinuities (i.e. bedding planes not being yet a mechanical plane
of weakness become a mechanical
plane of weakness) - material between rock blocks becomes weaker (remains of weathered material)
when a rock mass is weathered, there are: (3)
- Weaker rock blocks and soil grains;
- Smaller rock blocks and grains; and
- Lesser shear strength between blocks and grains.
what gives rock and soil masses strength
Rocks and soil masses consist of:
* intact blocks (rock) with discontinuities in-between (e.g. bedding plances, joints, fractures, etc.)
* grains (in soil) with grain contacts in-between
Strength of a mass is given by:
* strength (shear and tensile) of intact rock blocks or soil grains
* shear strength between blocks (rock) or grains (soil)
Weathering products from mechanical and chemical
weathering may accumulate on the Earth over bedrock . This material is called _____________.
regolith
are the upper layers of
regolith that support plant growth.
soil
soil profile
O horizon
A horizon
B horizon
C horizon
Typical mature soil consists of
several layers called ________
soil horizons.
Combination of O and A horizons
are called __________ .
topsoil
named for its
Organic component.
O horizon
mixture of humus, sand, silt, and clay. Also called zone of leaching .
A horizon
also called subsoil or zone of accumulation, is a transitional zone between topsoil and parent rock below.
B horizon
consists of partially weathered rock that grades into unweathered parent rock.
C horizon
degrees of weathering
- fresh
- slightly weathered
- moderately weathered
- highly weathered
- completely weathered
- residual soil
No visible sign of rock material weathering ; perhaps slight discoloration on major discontinuity surface
degrees of weathering
- fresh
Discoloration indicates weathering of rock material and discontinuity surfaces. All rock material may be discolored by weathering
degrees of weathering
2.slightly weathered
Less than half of the rock material is decomposed or disintigrated to a soil . Fresh or discolored rock is present either as a continuous framework or as core stones
degrees of weathering
3.Moderately weathered
More than half of the rock material is decomposed or disintigrated to a soil. Fresh or discolored rock is present either as a discontinuous framework or as core stone.
degrees of weathering
4.Highly weathered
All rock material is decomposed and/or disintigrated to soil. The original mass structure is still largely intact.
degrees of weathering
5.Completely weathered
All rock material is converted to soil. The mass structure and material fabric is destroyed. There is a large change in volume, but the soil has not been significantly transported.
degrees of weathering
6.Residual soil
