Exogenic Events - heavy rainfall or forest fire.
Geomorphic Threshold - threshold up to which landforms change before lurching into a new set of relationships, with rapid realignments of landscape materials and slopes. Pattern Sequence Over Time:
* Equilibrium stability.
* Destabilizing event.
* Period of adjustment.
* Development of a new and different condition of equilibrium stability. *Slow continuous events maintain an approximate equilibrium. *Dramatic events require longer recovery times before a new equilibrium is established.
Slopes - curved, inclined surfaces that form boundaries of landforms. A slope is 'stable' is its strength exceeds denudation processes. A slope is 'unstable' if materials are weaker than denudation processes. Weathering - rock disintegrates, dissolves, or is otherwise broken down. (physical, organic, chemical). Weathering is greatly influenced by the character of the bedrock. Regolith - partially weathered rock overlying bedrock, whether residual or transported. Bedrock - rock of the earth's crust that is below the soil and basically underweathered. It's the 'parent rock' from which weathered regolith and soils develop. Sediment - fine grained mineral matter that is transported and deposited by air, water, or ice. Parent Material - the unconsolidated material, from both organic and mineral sources, that is the basis of soil development. Joints - fractures or separations in rock without displacement of the sides; they increase the surface area of rock exposed to weathering processes. Important Controls on Weathering:
* climatic elements - precipitation, temperature, freeze-thaw cycles. * position of the water table and water movement on and within rock structures. * geographic orientation of a slope - north, south, east, west. * vegetation
* physical weathering dominates drier, cooler climates.
* chemical weathering dominates wetter, warmer climates. Sheeting - form of weathering associated with fracturing or fragmentation of rock by pressure release; often related to exfoliation processes. Exfoliation Dome - dome shaped feature of weathering produced by the response of granite to the overburden removed process, which relieves pressure from the rock. Layers of rock slough off in slabs or shells in a sheeting process. Physical Weathering - (mechanical) breaking and disintegrating of rock without any chemical alteration.
a) Frost Action - powerful mechanical force produced as water volume expands 9% as it freezes and can exceed the tensional strength of rock, breaking it.
b) Salt Crystal Growth - in arid climates, dry weather draws moisture to the surface of rocks. As water evaporates, crystals develop from dissolved minerals. When crystals grow they exert force.
c) Pressure Release Jointing - tremendous weight of the overburden is removed from the granite and the pressure of deep burial is relieved. The batholith responds with a slow but enormous heave. Chemical Weathering - decomposition and decay of the constituent minerals in rock through chemical alteration of those minerals. Water is essential, with rates keyed to temperature and precipitation values. Chemical reactions are active at microsites...