Erosion Features of Bryce Canyon Nat. Park in Utah
Slide 3
Definition of Weathering: Weathering = the breakdown of rock
due to physical and chemical changes, to produce smaller pieces.
(called fragments or sediments)
Slide 4
Physical Weathering: Physical (mechanical) weathering = changes
to the size and/or shape of rock (usually into smaller particles of
the same composition)
Slide 5
Types of physical weathering: Ice wedging water seeps into
cracks, freezes, expands and wedges the rock apart! Water and ice
are more powerful than rock over time!
Slide 6
Ice Wedging (Frost Action) Potholes in the road are examples of
the power of ice to wedge rock (or pavement) apart
Slide 7
Ice Wedging at Whistler Mountain, B.C., Canada
Slide 8
Types of physical weathering: Root action tree roots grow into
small fissures or wedges and expand rock
Slide 9
Root Actiontree roots are stronger than rock!!! They physically
break rock apart as they grow!
Slide 10
Some trees need virtually no soil to growand can live on bare
rock!
Slide 11
Types of physical weathering: Animal activity digging of
burrowing animals can break down rock Abrasion collision of rocks
with one another (especially in streams) breaks them down NOTE:
abrasion rounds off particles!! Exfoliation the peeling of rock due
to release of pressure experienced when rock was formed
Slide 12
Exfoliation (release of pressure) allows rock to expand when
exposed to Earths surface!
Slide 13
Chemical weathering Chemical Weathering = changes in the
chemical composition of rocks due to chemical processes and
reactions
Slide 14
Types of chemical weathering: Hydrolysis (hydration) minerals
react with and absorb water Example: feldspar reacts with water to
form kaolin (clay)
Slide 15
Types of chemical weathering: Carbonation carbon dioxide from
air reacts with water to create carbonic acid which breaks down
rocks (especially limestone, marble, etc.) NOTE: chemical
weathering typically results in a rounded appearance of the
landscapejust like here in the Catskills!
Slide 16
Types of chemical weathering: Oxidation rocks with metallic
elements combine with oxygen (in air and water) and rust away (rust
stains the rocks REDDISH BROWN)
Slide 17
Oxidation (water reacts with Iron)
Slide 18
Types of chemical weathering: Acid Rain: rain is naturally
slightly acidic, but industry has made it more so. Acids break down
rocks, especially carbonate rocks such as limestone. Carbonate
rocks = any rock containing calcium carbonate, which is the mineral
calcite (CaCO 3 ) Carbonate rocks react quickly with acids, and so
they will chemically weather away at a much faster rate than other
rocks IF plenty of acidic water is available!
Slide 19
Effect of Acid Rain on Carbonate Rocks: Cleopatras Needle while
in Egypt Cleopatras Needle now in NY City
Slide 20
Effect of Acid Rain on Carbonate Rocks
Slide 21
Types of chemical weathering: Plant acids some plants naturally
produce acids (humic acids) that seep into rock and cause chemical
weathering For example, pine needles can be very acidic and weaken
the rocks beneath them
Slide 22
Rate of Weathering Rate of Weathering how fast rocks break down
due to physical or chemical processes
Slide 23
Factors affecting rates of weathering:
Slide 24
Rock composition: Sedimentary rocks are generally soft and
weather fast. Limestone is easily dissolved by acids. Igneous and
metamorphic rocks are usually dense, hard, and more resistant to
weathering. Any rock containing quartz (hardness of 7) will
generally be resistant to weathering (conglomerate, quartzite,
granite, etc.)
Slide 25
Factors affecting rates of weathering Exposure to surface:
rocks exposed at surface weather much more quickly than buried
rock. Rock Outcrops are places where rock layers actually stick out
above groundwhere they are quickly exposed to lichens, moss, trees,
rainfall, ice, and animals!
Slide 26
Factors affecting rates of weathering: Climate: the amount of
precipitation and temperature are the most important factors.
Slide 27
Slide 28
Factors affecting rates of weathering: Surface Area as rocks
begin to break down into smaller pieces, they weather faster as the
total surface area of the rock is increased
Slide 29
Surface Area & Rate of Weathering:
Slide 30
Factors affecting rates of weathering: Topography higher
elevations tend to be colder and experience more freeze-thaw
cycles
Slide 31
Soil Soil is the result of weathering of rock, which produces
smaller pieces called fragments, which combine with organic matter,
air, and water to comprise soil. Soil = rock fragments, humus
(decayed plant and animal material), air and water
Slide 32
Composition of Soil.typical analysis
Slide 33
Transported & Residual Soils Residual Soil = soil that has
been left in place after bedrock weathers into smaller piecesso it
has the same composition as the underlying bedrock. Transported
soils = soil that has been brought to a location by wind, glaciers,
or rivers, so that the soil composition is different from the
underlying bedrock. Most of NYS soils are transported here by
glaciers moving south from Canadaso the soils are all mixed sizes
of sediment (pebbles, sand, silt, clay) and can be called glacial
till.
Slide 34
Glacial Till = mixed soil transported by glaciers during the
last ice age (12,000 yrs. Ago)
Slide 35
Soil develops slowly over time from bedrock.
Slide 36
Soil Horizons Soil separates over time into distinct layers as
follows: A horizon (Topsoil): the upper layer of dark brown soil
containing humus and plenty of animal activity (bugs, worms, etc.)
B horizon: also called subsoil, containing many more minerals
leached down by water infiltrating through the A horizon, so often
stained red by oxidation of iron minerals C horizon: made of
weathered bedrock (parent material) Usually contains larger
particles and rock fragments Bedrock: the underlying rock that is
still mostly un- weathered
Slide 37
Soil Horizons = layering of soils over time Soil Horizons
Slide 38
Soil Texture Soil texture = the relative amounts of SAND, SILT,
and CLAY contained in a given soil. Usually determined by
percentages of each sediment size.
Slide 39
What type of soil texture will the following soil compositions
produce? 2) 80% silt, 10% sand, 10% clay = _________________ 1) 20%
silt, 20% sand, 60% clay = ______________________ 3) 5% silt, 85%
sand, 10% clay = __________________________ 4) 40% silt, 20% sand,
______% clay = ____________________ 5) 45% silt, 10% sand, 45% clay
= ________________________ 6) 10% silt, 60% sand, 30% clay =
_______________________ 7) 60% silt, 20% sand, 20% clay =
______________________ Place the following points on the texture
triangle. A) 30% silt, 10% sand, 45% clay B) 0% silt, 20% sand, 80%
clay C) 15% silt, 30% sand, 55% clayD) 70% silt, 30% sand, 0%
clay