GEOl 101 Exam 4 Study Guide

Chapter 12 – Mass Wasting

• Factors affecting mass wasting;

  • angle of repose: steepest angle where a sloped surface is stable, determined by frictional forces between particles.

  • water: slightly wet material is cohesive, saturated material can lead to landslides due to loss of friction and increased weight.

  • vegetation: stabilizes slope using roots, absorbs water, removal of vegetation causes slop instability

  • soil/rock characteristics: properties such as grain size, shape, and distribution influence the stability, finer particles are easier to erode and larger particles provide better stability.

• Dip slope: what it is and can you identify it.

  • when slope id\s parallel to dip of rocks, direction the rock layers are inclined

• Natural and human-caused triggers of mass wasting.

  • natural: rainfall or snow fall, volcanic eruptions (adds material to slope, can melt glaciers), earthquakes, wildfires (removes vegetation)

  • Human: road building, removal of native vegetation (grass is often overwatered), house and other buildings

• Types of mass wasting: rockfall, slump, rockslide, debris flow, earth flow, creep. Be able to identify these in pictures or diagrams and understand the type of motion and characteristics of each.

  • Rockfall: happens over seconds or minutes, aided by frost action, forms talus slopes at base of slope

  • Slide: material is coherent, slides are intact, hold their shape

  • slump: movement over days to months, along a curve surface, common where base of slump is removed.

  • mudflows: not intact, mixture of water, soil, and rock flowing in a channel

  • earthflow: fluid movement of saturated silt and clay moving down a slope, more viscous

  • creep: very slow downslope movement, trees and fences bend, foundations break and crack,

Chapter 13 – Streams

• Stream characteristics; Be able to calculate gradient and discharge given stream info.

  • velocity: distance traveled over time, changes along length and width of stream, controlled by channel shape, velocity greatest in bend of a curved channel

  • gradient: vertical drop over a distance, similar to slope of line, changes along length of stream

  • discharge: volume of water moving downstream per time, constantly changing, discharge increases further downstream as tribuatries join in stream

    • Width X Depth X velocity or Area X velocity

• Base level and how changes to base level affects gradient, velocity, and stream processes.

  • base level: lowest point that stream can erode its channel, the end of the river

  • sea level is the ultimate base level

    • if base level rises or land drops, stream deposits material and creates a higher channel

    • if base level drops or land rises, a stream can erode their their valleys

• Suspended load and bed load

  • suspended load: sediment carried in suspension with water (silt, clay, and sand)

  • bed load: coarse grained material moved along bed of stream (gravel, sand, boulders

• Capacity and competence

  • capacity: maximum load of sediment that a stream can transport, determined by discharge

  • competence: maximum particle size that a stream can transform, determined by velocity

• Stream landforms:

  • point bars: deposition of inside edge of river bend

  • floodplains: valleys become wider as gradient decreases and steam meanders

  • deltas: fan-shaped deposit of alluvium formed where steam meets a lake or ocean

  • alluvial fans: fan shaped deposit at base of mountain, arid climates

  • oxbow lakes: when meanders merge and abandoned part fills with water

• Floods

  • most common and destructive of all geologic hazards

  • due to heavy precipitation, saturation of ground, topography, rapid snowmelt

Chapter 14 – Groundwater

• Water table

  • depth where rocks and sediment are saturated

  • elevation varies by location and by season

• Gaining and losing streams

  • gaining streams: groundwater flows into stream, water table will be higher than streams

  • losing streams: water flows from stream to groundwater, water table is lower than stream

• Porosity vs permeability

  • porosity: a measure of the void spaces in material

  • permeability: how easily a fluid can flow through that material

• Terms:

  • aquifer: geologic unit that stores and transmits groundwater

  • aquitard: geologic unit that limits groundwater flow

  • spring: where water table intersects ground

  • recharge: water entering aquifer, usually in mountains

  • discharge: water leaving aquifer, usually at a spring

• Types of aquifers

  • unconfined aquifer: no aquitard above aquifer, water is under pressure

  • perched aquifer: small aquifer that lies above main water table, has aquitard below it

• Wells and cone of depression

  • wells: pump out water faster than it can replenish

  • cone of depression: cone shaped area of lowered groundwater levels around a spring that’s being pumped

• Consequences of over-pumping groundwater

  • can create sink holes

  • can cause wells in coastal areas to pull seawater into well

  • contamination: pumping can reverse groundwater flow

• Caves and sinkholes

  • dissolution of limestone from carbonic acids forms caves

  • sinkhole: depressions caused by collapse as rock has been dissolved by groundwater

• Hydrothermal features

  • where hot water rises to surface

  • water is often mineralized so it precipitates minerals at surface

  • Geysers (periodic eruptions of hot water and steam) and fumaroles (erupts steam)

  • factors needed: large source of heat, permeable rocks connected to heat source to allow circulation, cap of low permeability rock