Gradation• Landforms are continuously changing:

Tectonic and Volcanic activity builds up the earth and gradation forces try to level the earth

• If Gradational forces worked alone, the earth would be leveled completely in 12 million years

Forms of Gradation Include:Degradation – Any process that wears away

or rearranges landforms. Includes: weathering, mass movements, erosion and transportation

Aggradation – Includes the deposition of eroded materials

Glaciation – Includes the movement of materials through glacier ice

**Streams and Rivers are the primary gradational forces in the shaping of our landscapes

Base Level

• The Base Level of a stream is the level below which a stream can no longer erode. The Ultimate Base Level corresponds to sea level.

• A local base level can be a result of an inland lake

• Artificial base levels result from the construction of man made structures such as dams that retard the natural flow of water creating a reservoir

Weathering

• Weathering encompasses a group of processes by which surface and subsurface rock disintegrates into mineral particles or dissolves in water

• Bedrock is the Parent Material from which weathered material or sediment is produced

• Two distinct types of weathering occur Physical/Mechanical and Chemical

Physical Weathering• The mechanical disintegration of rock

without any chemical alteration of the parent material

Frost Shattering – when moisture in cracks freezes the water expands, exerting pressure on the rock

Pressure

Physical Weathering

Crystallization – Similar mechanism to frost shattering but pressures result from the formation of salt crystals in cracks

Root Wedging – Plant roots can create enough pressure to crack rock

Thermal Expansion – when rocks under go

rapid changes in temperature the related stress can cause fracturing

Hydration – occurs where water is absorbed by a mineral. This addition of water initiates swelling and stress within the rock

Pressure-Release (sheeting/exfoliation) – rocks that form under tremendous pressures deep within the earth can slowly fall apart once the pressure is relieved

Chemical Weathering• The process by which rock is broken apart due

to chemical processes

• Chemical weathering attacks weaker minerals within rock, changing them to a vulnerable state and/or dissolving them in water

• Chemical weathering includes: Hydrolysis, Oxidation, Carbonation and Solution

More Weathering Examples

Slopes

• Material loosened by weathering is susceptible to erosion and transportation. However if it is to move down slope, friction, inertia and the cohesion of particles must be overcome

• Weathered sediment is classified due to its particle size

• Soil (mixture of sand and finer grain particles) Sand, and Gravel will be the sediment size classification used for this course

• The Angle of Repose is the steepness of a slope when lose material comes to rest

• This angle is dependant on sediment size and texture

Fine Sand Course Sand

Gravel

Mass Movements• Mass Movements are downward

movements of material propelled and controlled by gravity

• Classes of mass movements include: Fall, Slide, Flow, Creep