Transcript Review of ch. 4 and 5

Chapter 4: Weathering,
Erosion and Landscapes
Why do Rocks Weather?
• When rocks are exposed to different
environments, they begin to break down.
• Physical weathering is when the size and/or
shape of the rock changes due to forces upon it.
For example: tree roots, frost action/ice wedging,
abrasion,
• Chemical weathering is when a chemical
change results in different rock or mineral
composition. For example: rusting/oxidation of
iron or feldspar turns to clay.
• Chemical weathering is fastest in warm, moist
climates!
How do Soils Form?
• Soil is produced by weathering of rocks and
biological activity.
• Eventually, there will be several different soil
horizons. The top layer will be the “top soil” –
the one with the most organic (humus) material.
• Protecting the soil is important! Decrease
erosion, keep plants in place. Be careful about
over-using road salts and other poisonous
materials.
How are Weathered Materials
Transported?
• Broken rocks (sediments) are moved by forces
of erosion. These forces include gravity, water,
wind and ice.
• Gravity: mass movement/mass wasting –
materials slide down due to gravity alone.
Rocks are all jumbled, broken and angular.
• Water: running water is our most important form
of erosion in moist areas – like NY! Materials
are carried by rolling along the river bed,
suspension in the water, dissolved in solution or
flotation.
More about water erosion…
• Stream velocity: The faster water flows,
the larger particles it can carry. See p. 6 in
the ESRTs.
• When a stream meanders, the faster water
is on the OUTSIDE curve. The slower
water is the inside.
• The fastest water flow is just below the
surface in a straight part of a river.
Wind erosion…
• Smaller particles only.
• Wind erosion picks up loose materials –
where it is dry and there isn’t much plant
cover.
Erosion by ice….
• Glaciers are powerful enough to move ALL
materials!
• Moving large boulders over lower bedrock
can leave scratches (striations).
• U-shaped valleys are left by glaciers.
• Unsorted, unconsolidated sediments are
left when a glacier suddenly melts.
• If meltwater runs over the sediments, they
may become sorted.
Characteristic Changes Caused by
Agents of Erosion:
• Gravity: angular – not enough time to smooth
down. Piles at the bottom of hills.
• Running water: smooth and round – especially
when the water carries the rock along the bottom
(abrading the rock) for a long time.
• Wind: ventifacts are triangular…may have pits
from being sand-blasted. Only small particles
can be moved! May form sand dunes.
• Glaciers: striations, unsorted, loose. May have
LARGE boulders alone in a field.
What is Deposition?
• Sediments will eventually stop moving.
• Deposits can show characteristics that give
clues to how they were moved to their new
location:
– Gravity: angular, unsorted talus piles.
– Water: smooth, rounded. May form deltas (if particles
are small, like silt or clay!)
– Wind: small, piles, sand dunes that move with the
wind.
– Ice (glaciers): unsorted, unconsolidated, scratched..
Sorting of Sediments:
• Horizontal and vertical sorting happens
when the erosional force slows or
sediments fall down through water.
• No sorting with gravity and moving ice.
• Sorting will occur with running water and
wind….and with meltwater off of glaciers.
• The LARGEST, ROUNDEST and
DENSEST will be deposited first.
New York and Ice Ages:
• As recently as 20,000 years ago we were
covered in ice. (see the ESRTs pages 8
and 9)
• See p. 94 and 95 in the review bk. For
maps.
• Some features: U-valleys, polished
bedrock, grooves or striations (from
sediments dragged by the ice), drumlins
moraines, kettles.
Oceans and Coastal Processes:
• Ocean info can be found in the ESRTs.
• Also, illustrations are on p.98 and 99 in the
review book!
• Saving our shorelines from erosion is
extremely important see p. 98-100 in the
review book for examples!
What is a Landscape?
• Topographic relief (plain, plateau or mountains)
defines a landscape.
• See p. 2 in the ESRTs for the Landscape
Regions of New York.
• Climate plays a role in landscape development.
The arid areas have steeper slopes and sharper
angles because there is little weathering and
very little soil development! Therefore, there is
very little plant growth.
Geologic Factors and Landscapes:
• Resistance to weathering determines
whether a rock will be easily worn down or
not. The resistant rock is NOT worn down
as much and will therefore stick up more.
It will stick out at the sides of cliffs
(escarpments) or be at the tops of
mountains.
• Softer rocks are more easily worn away
and become the bottoms of valleys.
Landscape = Drainage Patterns:
• The way the land slopes and the presence
of low spots determines where the rivers
and their tributaries will flow.
• Figure 4-7 on p. 104 in the review book
shows some of these patterns.
• See the landscapes of NY map on p. 2
in the ESRTs and compare it to the
Bedrock map on p. 3 in the ESRTs.