Transcript Gradation
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 Course Sand Fine 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