Transcript Gradation Biotic and Chemical Weathering Geography 12 Ms. Inden Biotic Weathering • Plant roots work their way into cracks and force rocks to break apart –

Gradation
Biotic and Chemical Weathering
Geography 12
Ms. Inden
Biotic Weathering
• Plant roots work their way into cracks and force
rocks to break apart
– Some chemical reactions take place as well –
chemical weathering
• Animals burrow into ground
• Human mining activity
• Please note: Sometimes referred to as
biological weathering. However, biological
weathering refers at times to the chemical
reactions used to create soils (chelating) from
biotic weathering
Chemical Weathering
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Oxidation
Hydrolosis
Carbonation
Solution
Chelating
Acid rain
Limestone ‘pavement’ that has
been chemically weathered by
rain. Coming up: clints and
grykes! Watch for it.
http://www.earth.ox.ac.uk/~oesis/field/index.html
Oxidization
• Metals exposed to
air
• Oxygen dissolved in
water combines with
iron molecules to
form iron oxide – or
rust
• Red for iron, blue
green for copper,
Hydrolysis
• Carbonic acid acts on rocks containing silicon,
replacing the silicon with ions of water
• The rock falls apart, what is left is clay
• This is the chemical process that creates the
deep soils of the Amazon other rain forests
• feldspar creates clays and is the most common
weathering reaction on earth – that is why so
much sedimentary rock is clay
Chelating – really biochemical
weathering
• When decomposing organic matter in the
soil releases organic acids
• These acids attack certain minerals in the
rock and then release iron and aluminum
ions which can be transported away by
water
Carbonation
• Rainwater falls through the atmosphere
• Picks up/dissolves small amounts of CO2 gas
• The water is now a weak solution of carbonic
acid
• The calcium in limestone is dissolved by the
water and the rock erodes
• Other minerals in rocks are washed away this
way as well. This is called SOLUTION
– The most soluble elements in rocks are:
• Calcium, magnesium, sodium and potassium
Limestone – dissolved by solution
• Limestone is an organic
sedimentary rock, made
up of calcium carbonate
that comes from the tiny
shells and micro
skeletons that fell to the
sea bed
• Layers compressed
under softer conditions
create chalk, while
medium pressure creates
limestone and extreme
pressure forms it into a
metamorphic rock called
marble
Designed by Canadian
sculptor and architect
Walter Seymour Allward,
the monument took eleven
years to build. It rests on a
bed of 11,000 tonnes of
concrete, reinforced with
hundreds of tonnes of
steel. The towering pylons
and sculptured figures
contain almost 6,000
tonnes of limestone
brought to the site from an
abandoned Roman quarry
on the Adriatic Sea (in
present day Croatia).
http://www.vacacc.gc.ca/remembers/sub.cfm?source=memorials/ww1me
m/Vimy
Vimy Ridge
Memorial,
France
A cloaked figure stands at
the front, or east side, of the
monument overlooking the
Douai Plain. It was carved
from a single, 30-tonne
block and is the largest
piece in the monument.
This sorrowing figure of a
woman represents
Canada—a young nation
mourning her dead. Below
is a tomb, draped in laurel
branches and bearing a
helmet and sword.
Silt and Clay
• Mechanical
weathering creates
SILT, called LOESS
if deposited by wind
• Chemical
weathering creates
CLAY (hydrolosis)
Acid Rain
• Precipitation is already a little acid (think solution
and the dissolving of limestone)
• Can be caused by supervolcanic eruptions or
meteors and can cause severe environmental
damage in these catastrophic situations
• Today, human activities create acid deposition –
S02 and nitrogen oxide
– Smelting, burning fossil fuels, nitrogen oxygen from
automobiles
Effects of Acid Rain
• Limestone buildings
can be damaged
(weathered) by acid
rain, but the impact
on the natural
environment is huge
• Limestone helps to
neutralize the acid
rain somewhat, but
granite does not