Untitled Flashcards Set
Tectonic forces (uplit) and Surface process (wear land down) shape the earth’s surface.
Physical weathering are rocks broken down to smaller rocks.
Chemical weathering rocks broken down by composition
Types of Physical weathering
Abrasion (erosion)
Frost wedging (Water within fractures expands when it freezes)
Root wedging (Root growth exerts pressure on surrounding material forcing it apart)
Mineral wedging (minerals crystallize within pore spaces, apply pressure to the surrounding rock)
Dissolution - mineral bonds break (dissolved into solution)
Oxidation - metals react with oxygen (rock rusts)
Hydrolysis - reaction incorporating water (clay minerals form)
Oxidation produces mafic minerals such as hematite, limonite, and bauxite.
Hydrolysis produces feldspar minerals like clay minerals.
Weathering rind - Fractures as a weathering conduit
Spheroidal weathering - chemical weathering works from the corners and fractured edges of a rock toward the interior, form a rounded shape
Rock disintegration -rocks are made of interlocking minerals, when one of the component minerals dissolves away, the remaining rock structure is weakened
Differential weathering -various rock types have differing susceptibility to weathering processes
Factors of slow weathering process for rocks - Stable Mineralogy, Massive Rock Structure
Factors of slow weathering process for climate - Sparse Rainfall, Cool Temperatures
Factors of slow weathering process for surface conditions - Thick Soil Cover, Sparse Vegetation, Fewer Roots, Sparse Vegetation, Less Organic Acid
Factors of slow weathering in time - Limited Exposure
Factors of fast weathering process for rocks - Soluble Mineralogy, Fractured/Thinly
Bedded Rock Structure
Factors of fast weathering process for climate - Abundant Rainfall, High Temperatures
Factors of fast weathering process for surface conditions - Exposed Bedrock, Abundant Vegetation, More Roots, Abundant Vegetation, More Organic Acids
Factors of fast weathering in time - Extended Exposure
Common soils are 45% regolith, 5% organics, and 50% porosity containing either air or water
Residual soil stays over its parent rock.
Transported soil forms from particles from another place.
Steep slopes tend to have less soil development
Living organisms impact organic content, help break matter down, and can aid in soil development
increased time leads to increased weathering, thicker soils, and more mature soil development
Soil Horizons - Layering of regolith and organic matter between the underlying bedrock and the Earth’s surface will develop over time depending on the various soil development controls
Pedalfer
* Form in temperate climates with moderate rainfall
• Soil is grey and clay-rich, fertile
• Common in forest and grassland areas
Pedocal:
• Form in arid or desert climates with little rainfall
• Soil is characterized by less clay and organic matter
• Evaporation draws water and minerals up through to soil
Laterite:
• Forms in a hot, humid climate with abundant rainfall (severe chemical weathering)
• Soil is deep, red, hard, and infertile
• Plants recycle nutrients from a thin O/A horizon; deeper soil is nutrient poor
Mass Wasting: The downslope movement of earth materials (rock, regolith, and soil) under influence of gravity.
Gravity moves all material to the lowest possible elevation.
Gravity acts normal to the slope, stabilizing the object against the slope.
Gravity acts parallel to the slope, driving the object down slope
Consolidated - block of material resting on a slope
Friction is largely the result of surface roughness.
Unconsolidated - material like regolith and soil
The ability of the material to resist down-slope movement is referred to as its shear strength.
Water tends to stick to particles through surface tension
There will come a point when surface tension no longer holds grains together. Excess water in pore spaces can force unconsolidated grains apart, decreasing internal friction and reducing the material’s shear strength
Pore water pressure is the force water exerts on the surrounding grains.
Angle of Repose: is the maximum angle at which a sloping surface formed of dry, unconsolidated, granular material is stable. The closer to this angle, the more unstable the material
Vegetation: plant roots serve to absorb surface water and bind unconsolidated material, increasing its shear strength.
Triggering a landslide is adding energy that helps material overcome inertia and friction, leading to failure.
Classification of Mass Wasting
Fall - free fall of detached particles from a steep slope
Slide - mass remains intact, moving over a defined surface
Consolidated: bedrock or well bonded soil (vegetated); internal shear strength resists movement
Translation – slip along a planar surface
Rotational – slip along a curved surface
Flow - moves as viscous fluid, usually water saturated
Unconsolidated: loose regolith and soil; impacted by particle size, shape, and water content
Debris - dominated by coarse fraction
Earth - dominated by sand, silt, clay (soil)
Mud - dominated by fines (clay/silt) and water
Creep- results from expansion and contraction (wet/dry and freeze/thaw cycles)
Solifluction
• Flow of water saturated soil over impermeable material
• Common in cold climates where deep soil remains frozen (permafrost) while water in upper soil melts
• Surface vegetation remains intact, resulting in a wrinkled surface as soil moves
Earthflow
Flow of fine-grained materials that have been saturated with water - intermediate between creep and mudflow.
• Common where soil is thick and rainfall is abundant
• Can start as coherent slides that break up and begin to flow as a very viscous fluid
• Hummocky, lobate topography at the toe of the feature where soil accumulates
Mudflows are fast, water saturated, composed mostly of particles
smaller than sand (consistency of wet concrete - up to 30% water),
commonly channelized, follows heavy rains, often on sparsely
vegetated slopes (deserts, wildfires, volcanoes)
Debris flows occur on steep slopes, are fast, composed of coarse
debris (boulders+), and can be dry (slower, short distance
movement similar to earthflows) or water saturated (faster, long
distance movement similar to mudflows)
Avalanches: downslope movement of
snow, ice, and rocks
• Many of the same factors the influence
movement in unconsolidated earth
materials applied to snow and ice.
• Once moving, an avalanche moves
quickly down a slope partly because it
traps a layer of air beneath the flow. This
reduces friction with the slope surface
and increases the flow speed.
Avalanche chute
Turbidity Flows
Dense, sediment laden water rushes
from the continental shelf, down the
continental slope, and onto the rise
and abyssal plain (deposits are called
turbidites).
Like avalanches, these flows move
quickly because they flow above the
slope surface, minimizing friction.
PREVENTION
In many cases, the best solution is avoidance. Geologists look for
evidence of past movements (landforms) or detect regions that
are beginning to move. Certain steps can be taken to remediate
the problem and stabilize the slope.
Preventing a landslide will involve reducing the driving force
and increasing the resisting forces (shear strength).
• Reduce slope
• Reduce water
• Reduce weight
• Remove loose material
• Increase vegetation
• Add base support
• Careful geotechnical planning
Several factors control the amount of runoff vs. infiltration:
• Surface permeability (low permeability, high runoff)
• Slope angle (high slope, high runoff)
• Amount and type of vegetation (low vegetation, high runoff)
• Soil moisture (high soil moisture, high runoff)
• Rainfall intensity & duration (high intensity & duration, highrunoff)
A drainage basin is a precipitation catchment area or watershed for a given river.
Base level is the lowest level
to which a stream can erode;
controlled by the elevation of
the stream mouth (commonly
sea level)
3 zone of a river are headwaters zone, transfer zone, and depositional zone
Vertical erosion dominant, downcutting
and mass wasting creates V-shaped valley
Most drainage systems start with erosion near the
mouth and work their way toward the headwaters, a
process known as headward erosion
• Implement sustainable water management practices