Erosion and WeatheringErosion and Weathering

Erosion - the removal and transport of earth materials by natural agents. Some of these agents include glaciers, wind, water, earthquakes, volcanoes, tornadoes, hurricanes, mud flows, and avalanches.

GlaciersGlaciers• Glaciers have caused extensive erosion in the northern

United States and around the Rocky and Cascade Mountains.

• There are two different ways in which glaciers cause erosion, by removing material and by depositing materials.

• Some features caused by glaciers are: • horns (pyramid shaped peaks) • arêtes (knife shaped ridges) • cirques (a bowl shaped depression found in mountains) • erratics (boulders ) • valleys • tunnels • lakes.

VolcanoesVolcanoes

• Volcanoes are the primary natural disasters noted for erosion. They take materials from inside the earth and spread them on the surface. The volcano can eject these materials in several different forms:

• Lava• Pillow lava• Tephra which includes all sizes of solid

fragments of lava from ash to blocks. • Pyroclastics

EarthquakesEarthquakes

• Earthquakes may not seem like an example of erosion, but they can be considered as one. Earthquakes include

• the mass movement of rock • friction between plates can wear away and

transport materials to a new location • the shaking may initiate mud flows or

avalanches that can be very hazardous to animals and plants alike.

Tornadoes and HurricanesTornadoes and Hurricanes

• Tornadoes and Hurricanes could be included with wind and water erosion.

• They accelerate the effects that wind and water have on land forms.

• The wind speed in tornadoes can reach 500 km an hour and hurricanes have wind speeds over 140 km per hour.

• These terrifying winds can move materials, such as boulders, rocks, sands, and soils.

WindWind• Wind is one of the primary eroders, next to

water. Wind can erode by: • Abrasion - Sand grains are the best tool in

abrasion, because it is made up of hard minerals, like quartz. Desert sand blasts can grind down boulders, usually into a smooth face or facet

• Deflation - the process in which winds remove loose rock particles from the surrounding area

• Deposition - depositing of sediments as well as removing them.

WaterWater• The two main types of water erosion are that by streams

and that by waves. • Stream erosion - can carry and deposit material, running

water in a stream can carry materials that attack the bedrock of the river and create deeper valleys, materials are then deposited at the mouth, or end of the river, usually to form a delta. 

• Waves erosion - storm waves can strike rock cliffs with a force of thousands of kilograms per square meter, bedrock can be split by water forced into cracks and fissures, or scoured away by the grinding of sands and pebbles, when waves break they cut away rock up to their highest level and create an overhang, which eventually creates a sea cliff.

Weathering is similar to erosion in that it includes the breakup of rocks, just not the transportation of the materials. The specific definition of weathering is: the breakup of rock due to exposure to the atmosphere.

Chemical Weathering, also known as decomposition, is when a rock's minerals are changed into different substances. Chemical processes include acid rain, acid etching by plants, oxidation, and demineralization by water More than one of the processes can occur simultaneously.

Elements Required for Chemical Weathering:

-oxygen, carbon dioxide and other gases from the atmosphere -water from rain and snow -minerals.

• Carbon dioxide is dissolved in water and forms carbonic acid• When Calcite is exposed to this acid it turns into calcium bicarbonate • Calcium bicarbonate is soluble and is carried away by water• Broken up pieces of rock are left behind

Solution

Sink hole near Stephenville, Western Newfoundland

• Ions of water replace ions of silicate• The rocks fall apart and the small ones are carried away• Clay is left behind – Bay of Fundy

Hydrolysis

• Occurs mostly in igneous and metamorphic rocks• Oxygen is dissolved in water and turns iron into iron oxide• The iron oxide is washed away• What remains is reddish brown stained rock – can be seen all around Clayton Park

Oxidation

Valley of Fire, NevadaValley of Fire, Nevada

Mechanical weathering takes place when rock is split or broken into smaller pieces of the same material without changing its composition.

Mechanical processes include flash floods, landslides, creep, exfoliation, root pry, frost action, mud slides, abrasion, mass wasting, undercutting, avalanches, and glaciers

Mechanical Weathering

Frost Wedging• Frost wedging is caused by the repeated freeze-thaw cycle of water in extreme climates • Most rocks have small cracks in them, called joints (or, tectonic joints). When it rains, rainwater seeps into these joints. As the day cools and temperatures at night drop below freezing, the water inside the joints freezes. • As water freezes into ice, it expands. • The expanding ice places pressure on the joints in the rock. Finally, when the pressure is too much, the joint expands.

Root Prying

Roots force their way soil and rocks causing rocks to split apart

Roots force their way under rocks pushing them to the surface and apart from one another

Thermal Expansion• Exists in climates where there is extreme hot and cold temperatures

• Rocks become very cold at night (desert) and then are heated in the daytime by the sun

• The rocks expand when they are heated and shatter

Exfoliation or Sheeting• Rocks that are formed under great pressure within the earth (Metamorphic) come to the surface of the earth

• The pressure is no longer present, so the rocks fall apart

• Usually in sheets, or layers

• This process is very common in Canada especially in the Canadian Shield