GradationBiotic 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

• 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.vac-acc.gc.ca/remembers/sub.cfm?source=memorials/ww1mem/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