From ESPRIT email:
David Kolodney mrkolodney@gmail.com
Leveling forces on Earth’s surface:
Tectonics raises mountains. Both the Himalayan and Adirondack
mountains are still growing, and yet they don’t get any taller. The
Catskills aren’t really mountains at all, they are a badly torn up
part of the Allegheny Plateau. Forces are always at work on
earth…..
Weathering, erosion and deposition overview:
Weathering is the breaking down of rock into sediments
Erosion is the transport of sediments
Deposition is the process of sediment build-up when dropped
Weathering:
Process of breaking rock down by chemical and/or physical
changes.
The type of weathering common in a location is determined
primarily by climate.
From http://en.wikibooks.org/wiki/High_School_Earth_Science/Weathering
1. Physical weathering: simply making the pieces smaller.
Causes:
a. Pressure unloading: when bedrock formed at great depth
is brought to the surface,
Usually by a combination of tectonics uplifting and
weathering. Exfoliation and jointing often occur.
b. Ice Wedging and frost action occur when water seeps into
the ground and later freezes. Freezing water expands
causing the rocks/soil to move apart.
c. Abrasion occurs when hard materials smash and break
other materials during erosion. Often water carries sand
that continuously scours and smooths rocks.
d. Plant Action occurs as the root tip moves into a crack and
the root continues to grow and widen, pushing the rock
apart.
e. Wetting and Drying causes rocks to first expand
(wetting) and then contract (drying), which makes the
rock brittle. Happens especially in areas with monsoons
and mud. A similar effect occurs when materials are
alternately heated and cooled, such as happens from
summer to winter or, in deserts, from day to night.
Effects:
a. Primarily, physical weathering increases the surface area
of a rock, allowing weathering to occur at a faster rate.
2. Chemical weathering occurs when there is an actual change in
the material due to a chemical reaction.
a. depends almost entirely on climate and rock material.
b. Water and heat are required, so it occurs mostly in moist,
warm climates.
c. Carbonic acid is released during the chemical breakdown
of calcite. Rust is formed during the chemical hydrolysis
of iron-bearing minerals.
d. Carbon dioxide is actually used during chemical
weathering, which some scientists say could have a
cooling effect on global temperatures.
3. Factors that Affect Weathering Rates:
a. Particle size/Surface area: when particles are broken
into smaller sizes, weathering becomes faster.
b. Chemical composition: as you know from Moh’s
hardness scale, not all materials are equally hard and
resistant.
c. Climate: chemical weathering is best in warm, moist
climates. Frost action requires changes in seasons.
d. Length of exposure to surface weather and conditions.
Erosion:
the _____________________ of weathered material
(_________________________) by an agent of erosion. These
include: gravity, running water, glaciers, waves and wind.
1. The _______________that powers erosion is usually
GRAVITY.
2. The __________________ of the agent of erosion
determines how ____________and dense the sediments
will be that it can carry. __________________________
rivers, etc can carry large/dense materials.
3. The primary agent of erosion on earth today is
__________________ water.
Deposition:
Build up of __________________ when an agent of erosion can
no longer carry them.
1. _________________________________: when the
erosive agent carrying the materials ______________
down (in running water, wind, waves), then the sediments
drop out according to their _______________ or their
densities (gold deposits in river beds) . (most common
earth materials are about the densities)
2. Particles can become sorted by size and smoothed and
rounded due to _______________________
3. If the sediments are dropped very abruptly/quickly (by
waterfalls, at edge of glaciers, directly by gravity) the
sediments will be ___________________.
Main Agents of Erosion and Deposition:
1. GRAVITY: rocks _____________ and are
_________________________at the base of mountains.
Sediments are never ________________ by size or shape. Talus
slopes are formed from this material, which can become
__________________.
3. Wind Erosion: carries _________________ particles, such as
sand, and these act like ______________________ paper.
a. causes the rocks to have a __________________ or frosted
appearance, as if they’ve been sandblasted.
b. leaves the particles _______________________ by size, and
rarely carries particles larger than __________________.
c. creates strange shapes, such as hoodoos and
_____________________
d. dunes show direction of wind movement, with a gentle slope
windward and a sharp slope ______________________.
e. Wind erosion is the most important agent of erosion in areas
with _________________climates, and flat terrain.
f. _____________________is an accumulation of wind blown
sediment of very fine, _____________ materials. Fine glacial
sediments blew across our country and much built up in the
southern states and plains.
3. Waves: carry sand and smaller particles to, from and along the
_____________________.
a. ocean waves are powered by ___________________across
the water. Waves transfer _________________________.
b. The speed of waves depends on the
__________________of the wind
Distance over which the wind
______________________ (fetch)
Length of __________________ the wind blows
c. Waves _______________________ when the depth of the
wave is ½ the wavelength. The energy changes from a
horizontal to _____________________ position and gravity
pulls the ‘breaker’ down.
There is increasing friction between the ‘trough’ of the wave
and the sand, slowing the bottom of the wave, while more
energy is given to the ‘top’ or crest.
d. Water waves are primarily ________________________
waves, in which particles move up and down while the wave
travels in a horizontal direction.
e. Longshore _________________________ occur due to the
combined actions of the _________________________
incoming wave and the straight-moving outgoing
______________________. The net effect of these motions
is to carry the sediments down the beach,
___________________to the beach as pushed by wind.
f. _________________________, breakers, and other human
obstructions are designed to alter the
____________________________ current and keep the sand
in one area. This can have devastating effects further down
the beach.