2. Weathering
• Weathering- breaking down of rocks and
other materials on the Earth’s surface.
– Effects all substances exposed to the atmosphere.
• Weathered bricks on buildings are darker in color and
has rounded edges.
• The piles of rock at the base of a mountain is caused by
weathering.
– Effects are not always easily observed.
3. • Two types of weathering
• Mechanical weathering- weathering that does
not involve changes in the chemical makeup
of rocks.
• Chemical weathering- weathering that
involves changes in the chemical makeup of
rocks.
4. Mechanical Weathering
• Rocks are broken into different shapes and
smaller pieces.
– At the beginning of the process, typical rock fragments
are sharp and angular. As weathering continues, they
become smooth and rounded.
• Temperature- rocks can be broken apart by
changes in temperature.
– Heating and cooling cycle.
• Exfoliation- the breaking off of curved sheets or
slabs parallel to a rock’s surface due to
weathering.
5.
6. • Frost action- the breaking apart of a rock
caused by the water freezing and expanding
within cracks.
– Occurs when water seeps into a small opening or
crack in a rock. When the temperature falls below
0o C, the freezing point of water, the water in the
crack freezes and expands. The crack in the rock is
made larger by the pressure of the expanding
water. In time, the freezing and melting of the
water cause the rock to break into pieces.
7.
8. • Organic activity- plants and animals can cause
mechanical weathering.
• The roots of plants sometimes loosen rock
material.
• A plant growing in a crack in a rock can make
the crack larger as the plant’s roots grow and
spread out.
• Root-pry- is an organic activity, or an activity
caused by living things.
9.
10. • Gravity- sometimes pulls loosened rocks down
mountain cliffs.
• Landslides- a large movement of loose rocks
and soil.
– As the rocks fall, they collide with one another
and break into smaller pieces. Falling rocks
generally occur in areas where a road or highway
has been cut through a rock formation, leaving
cliffs on one or both sides of the road.
11.
12. • Abrasion- is the wearing away of rocks by
solid particles carried by wind, water, or other
forces.
– Wind- in desert areas, the wind easily picks up and
moves sand particles.
– Water- rivers carry along loose rocks and other
particles. The moving rocks and particles collide,
scrap against one another, and eventually break.
13.
14. Chemical Weathering
• Weathering that changes the mineral
composition of the rock.
• As chemical changes take place, minerals can
be added to or removed from rocks.
• The minerals in rocks can be broken down in a
process called decomposition.
15. • Water- can cause chemical weathering when
combine with other things.
• Can dissolve most of the minerals that hold rocks
together.
• Water can form acids when it mixes with certain
gases in the atmosphere.
– Acids often speed up the decomposition of rocks.
• Water can also combine with a mineral to form a
completely different mineral.
– When the mineral feldspar reacts with water, it forms
clay.
16.
17. • Oxidation- is the process in which oxygen
chemically combines with another substance.
• The result of oxidation is the formation of an
entirely different substance.
• Iron in rocks combine with oxygen in the air to
form iron oxide, or rust.
• If oxidation is taking place, the inner material
of a rock will be a different color from the
outer material.
18.
19. • Carbonation- the process in which carbonic
acid reacts chemically with other substances.
• Carbon dioxide dissolves in water, a weak acid
called carbonic acid is formed.
• In nature carbonic acid is formed when carbon
dioxide in the air dissolves in rain.
• Carbonic acid slowly decomposes feldspar and
limestone.
20. • Sulfuric Acid- the air in certain areas is
polluted with sulfur oxides. Sulfur oxides are
the byproduct of the burning of coal as a
source of energy.
• Sulfuric acid corrodes, or wears away, rocks,
metals, and other materials very quickly.
21. • Plant Acids- certain types of plants can cause
chemical weathering.
• Mosses produce weak acids that can weather
certain types of minerals in rocks.
• Mosses can gradually dissolve minerals and
break rock into smaller pieces.
• Lichens also produce weak acids that break
down the minerals in rock.
22. Rate of Weathering
• Stable rock- a rock composed of minerals that resist
chemical weathering.
• Factors of Weathering
– Composition of rocks
• Two different types of rocks in the same climate can weather
differently.
– Time the rock is exposed
• A very old rock that has not been exposed to the various forces of
weathering can remain almost unchanged. But if a newly formed
rock is immediately deposited on the Earth’s surface, it will begin
to weather right away.
– Exposed surface area
• The more surface area that is exposed the more weathering takes
place.
