Transcript Mechanical Weathering

© Copyright 2004 - 2005. M. J. Krech. All rights reserved.
Mechanical
Weathering
 Disintegration – breaks down into smaller
pieces, no new substance
Frost Action
or
Ice Wedging
Frost Action
 Ice expands when frozen and cracks rocks
 Causes pot holes in winter
 Happens where the temperature goes both
above and below the freezing point of water
 Called Ice Wedging
Abrasion
Wind Abrasion
Wind blows sand which wears away cliffs
Water Abrasion
Water carries rocks along in streams & rivers which
collide and become smoothed into rounded river
rocks
Gravity
Landslides
 Gravity pulls rocks loose
 They break apart as they fall downhill
Organic
Activity:
Root Pry
Root Pry
 Roots expand as they grow and crack rocks.
 Other organic activity
 Ants, woodchucks, and worms dig holes
that let in water that causes weathering.
Wetting and
Drying
Rocks that contain CLAY swell and
shrink as they absorb water then dry
out, thus cracking the rocks
Joint Sheeting
As top soil erodes, rock layers
below expand and crack into layers
Called EXFOLIATION when large
sheets of rock break away at the
surface
Chemical
Weathering
Decomposition –
breakdown into new
substances
Hydrolysis
The chemical action of water
with other substances
Example: Feldspar turns into
clay
Feldspar +Water = Clay
Feldspar
A Clay Cliff
Plant Acids
Acids given off by lichens
and mosses eat at rocks
Sulfuric Acid
ACID RAIN: Sulfuric acid
causes blurred words on
gravestones and monuments
Photo taken 100 years ago
Photo taken recently
Both of these are Civil War headstones.
Why has one weathered more?
1865
1862
Oxidation
RUST caused by oxygen
combining with iron-bearing
minerals in rocks causes red
bands on limestone cliffs
Carbonation
Carbon dioxide combines with
water to form carbonic acid
which eats away layers of
limestone rock
Forms CAVES; KARST
TOPOGRAPHY
Karst Topography
 A type of landscape in rainy regions where there is
limestone near the surface, characterized by caves,
sinkholes, and disappearing streams.
 Created by chemical weathering of limestone
Features of Karst: Sinkholes
Features of Karst: Caves
Features of Karst: Disappearing
Streams
The end.
© Copyright 2004 - 2005. M. J. Krech. All rights reserved.