Geography 12: Unit Four

Erosion and Weathering

Upcoming tests December 28 Term Paper January 4th, 2011

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erosion and weathering are part of the forces of gradation which do battle with tectonic forces

Erosion: Denudation by wind, water, or ice, which dislodges, dissolves or removes surface material

Denudation: any process that wears away or rearanges landforms.

Weathering: either disintegrate rock into mineral particles or dissolve them in water.

Tectonic Forces: Strive to build up rock structures

Introduction

Strive to build up rock structures

Tectonic Forces

strive to bring rock structures to a level or a uniform slope; this can be done in two ways--by tearing down (i.e. degradation or erosion) or filling in (i.e. aggradation or deposition)

Gradational Forces

erosion can be divided into two processes: a) the breaking up of rock masses (i.e. weathering )b) the carrying away of the weathered rock fragments (i.e. transportation )

Erosion

weathering, transportation, and deposition

Deposition is the geological process by which material is added to a landform or land mass

Cycle of Gradation

When rock is broken and disintegrated without any chemical alteration.

By, breaking up rock, physical weathering produces more surface area on which chemical weathering can operate

Page 421-422 of Text

Physical Weathering

When water freezes, its volume expands as much as 9%. This mechanical force is called frost action

Frost: Expanding.....

Thawing: Contracting

Causes rocks to split apart

Frost Action

tree roots, for example, growing down into cracks can exert powerful forces- even mosses and lichens can help to split rocks apart

Lichens:Any of many symbiotic organisms, being associations of fungi and algae

Plants and Roots

Salt- Crystal growth

Dry Weather draws moisture to the surface of rocks

Water evaporates , dissolved minerals in the water grow crystals

The crystals enlarge and exert a force great enough to break up the rock

P.423

Physical Weathering

Exfoliation

- in humid climates, running water tends to round off the surface features causing the "skin" of the rock to peel off- this is also an important form of weathering in desert areas where the daily temperature range can be high

Physical Weathering

Exfoliation Dome: A dome shaped feature of weathering, produced by the response of granite to the overburden removal process.

See page 424 for image

Key Term

is the breakdown of rock into smaller particles due to such factors as freezing and thawing, release of pressure, water absorption, salt crystal formation, landmass uplift, expansion and contraction from the sun or fire, plant root growth, actions of animals, abrasion, or other means that do not directly affect the rock's chemistry.

Physical Weathering

the decay of rock through actual chemical change in the composition of its minerals- most common in warm and humid climates where both water and heat speedup chemical reactions

Chemical Weathering

occurs especially with rocks containing salt minerals- water is absorbed into the internal structure of the rock causing swelling and making it vulnerable to breakdown due to pressure and potential chemical structure changes- a physio-chemical processeg gypsum results from water being added to anhydrite (CaSO4)

Hydration

It converts feldspar, into clay and silica

Feldspar: a group of rock forming minerals which make up 60% of the earths crust

Silica: Sand

Hydration

hydrolysis - occurs especially with granite- causes rock to whiten (erodes slowly)- creates clay

Breaks down minerals in rocks Hydration: Water combines with minerals in

the rock, the hydrolysis process involves water and elements in chemical reactions to produce different compounds

Hydrolysis

Certain metallic elements combine with oxygen to form oxides.

creates rusty red rock occurs especially with rock

containing iron nitrate erodes and forms soil See Page 426: Pictures A and B

Oxidation

occurs with limestone (easiest to erode)- ground water absorbs carbon dioxide to form a slightly acidic solution- destroys joints (joint: line of weakness in a rock) and bedding planes to form karst topography

Dissolution of Carbonates

Karst: A word from Slovenia which means “Dissolvable rock”

Topography: the surface shape and features themselves

Page 427-431

Karst Topography

Karst is a distinctive topography in which the landscape is largely shaped by the dissolving action of water on carbonate bedrock (usually limestone or marble).

Karst Topography

For limestone landscape to develop into karst topography there are several conditions:

Limestone formation must contain 80% or more calcium carbonate

Complex patterns of joints are needed for water to form routes to subsurface driainage channels

Formation of Karst

There must be an aerated(containing air) zone between the ground surface and the water table

Vegetation cover is required

Formation of Karst

Karst occurs in Arid areas.

Arid: Lacking moisture, especially having insufficient rainfall to support trees or woody plants

Role of Climate

Sinkholes: Nearly circular depression created by the weathering of karst landscapes with subterranean drainage. Also, known as a doline.

Subterranean: underground structures, both natural and man-made. Ex> Cave

Results of Karst Topography

Sinkhole

A complex landscape in which sinkholes is referred to as cockpit karst.

Sinkholes

Any unit movement of a body of material, propelled and controlled by gravity

Also known As Mass Wasting: the downhill of weathered materials resulting from the pull of gravity.

Mass Movement

Creep Flows Slides Falls

Planet Earth Text Book: 249

Common forms of mass wasting

A persistent gradual mass movement of surface soil is called soil creep

Caused by freeze-thaw cycle

See page 439 of Geo Text

Creep

Solifluction: is used to describe a slow downhill flow of water-saturated rock and soil materials

Solifluction common in cold climates Ground beneath is permanently

frozen Can cause Avalanches

Flows

The simplest form of slide is called a rock slide

Debris Slides: are caused when loose rock and soil in steeply sloping terrain are shaken loose by an earthquake, river or glacial erosion. Such slides move rapidly downhill

A block of soil that makes a rotational slip along a concave surface is known as a slump.

Slides

High Mountains Frost Shattering Thumbling Rubble known as talus or scree Talus: Bigger rocks Scree: smaller debris...Basically the

same thing

Falls

What evidence of weathering have you seen?

Class Questions