Geo C.O.4

Mass Wasting

downward movement of rock and soil on a slope, primarily driven by the force of gravity.

Mass Wasting

with proper planning, the most easily avoidable of all major geologic hazards

Mass Wasting

Various forms of mass wasting: rock falls, slumps, debris flows

Gravity

• Driving force for mass wasting
  ○ Normal force
  ○ Shear force
  ○ Shear resistance

Slope Angle

Steeper slope = higher shear force (less stable)

Rock Type

Loose debris = less stable than solid rock

Vegetation

Roots hold debris together

Climate

freeze/thaw = expansion/contraction lifts materials

As water content increases

shear strength decreases

Stress

is transferred from clay to fibers, which have excellent tensile strength

Stronger bond between clay and fibers

= higher reinforcing effect

Shear Strength

resistance to movement or deformation

Shear Strength

Saturated soil has reduced shear strength due to increased pore pressure

Shear Strength

Small amount of weather can prevent downslop movement (building a sandcastle)

Mass Wasting Triggers

Increased water content within the slope is the mose common

Mass Wasting Triggers

• Seismic (earthquake) activity

• Heavy rainfall

• Construction

• Lack of vegetation (no roots to hold rock/soil in place)

Fall

Flow

Trans

Rotational Slide(Slump)(pic)

Rate of movement

1cm/year -> 100km/hour

Solid bedrock or debris (unconsolidated material at Earth’s surface)

Type of material

Creep

very slow downslope movement of soil

Creep

Major contributing factors include water in soil and daily freeze-thaw cycles

Creep

Can be costly to maintain homes on creeping ground as foundations, walls, pipes and driveways crack and shit downslope over time

Flow

descending mass moves downhill as a viscous fluid

Earthflow

debris moves downslope, slowly or rapidly, as a viscous fluid

Debris Flow

flowing mixture of debris and water, usually down down a channe

Mudflow

only soil and water

Debris Avalanches

very rapid and turbulent

Solifluction

Flow of water-saturated debris over impermeable material

Solifluction Permafrost

common in colder climates

Slide

downward movements of soil or rock along a surface and can vary in depth, being either deep-seated or shallow

Translational slide

movement along plane parallel to motion

Rotational slide (slump)

movement along a curved surface

Rockslide and rock avalanche

the rapid sliding of a mass of bedrock along an inclined surface of weakness

Underwater landslides

turbidity currents

Underwater landslides

Can create a tsunami

Fall

sudden rock movements that detach from steep slopes or cliffs

Rockfall

a block of bedrock breaks free and falls or bounces down a cliff (commonly an apron of fallen rock fragments (talus) accumulates at cliff base)

Preventing Landslides

1. Modifying slope geometry to create more stable conditions
2. Using chemical agents to strengthen and reinforce the slope material
3. Installing structures like piles and retaining walls to provide stability and support
4. Grouting rock joints and fissures to improve rock mass cohesion
5. Diverting debris pathways to prevent material from accumulating on hazardous slopes
6. Rerouting surface and underwater drainage to minimize water-induced instability

Seasonal Flooding

Often arises from spring rains or melting of snow

Seasonal Flooding

Leads to increase in flow of rivers

During a flood event

river /stream’s channel becomes inundated -> water spills to adjacent floodplain -> speed decreases -> capacity to carry sediment/materials diminishes

Hydrologic Cycle

Encompasses processes which water moves from land to ocean surfaces to the atmosphere & returns in form of precipitation

atmosphere & precipitation

Encompasses processes which water moves from land to ocean surfaces to the _____ & returns in form of _____

land to ocean

Encompasses processes which water moves from _____ to _____ surfaces to the atmosphere & returns in form of precipitation

Hydrologic Cycle

Relies on various factors and is influenced by both oceans and land surfaces

Hydrologic Cycle

Represents continuous circulation of water on the plant

Hydrologic Cycle

Playing a vital role in regulating distribution and availability of water resources

Hydrologic Cycle

Distribution of water in the atmosphere

96.5%

Oceans

1.76%

Glacial ice

1.70%

Groundwater

0.014%

Lakes & Streams

0.001%

Soil moisture

98.8%

Glacial ice & groundwater contains _____ of the freshwater on Earth

Evaporation

Water vaporizes from the surfaces of water bodies & from moist soil and vegetation into the atmosphere

Precipitation

Water is released from the atmosphere in form of rain, snow, sleet/hail & falls back to the Earth’s surface

Runoff

Portion of precipitation that does not infiltrate the ground & flows over the land surface, eventually reaching water bodies

Infiltration

Water that penetrates into the soil & moves into underground aquifers

Transpiration

Water taken up by plants from soil released into the atmosphere as water through stomat

Running water

• Stream

• Headwaters

• Mouth

• Channel

• Stream banks

• Streambed

• Floodplain

Stream

Body of running water confined to a channel that runs downhill under the influence of gravity

Headwaters

Upper part of stream near its source in the mountains

Mouth

Where a stream enters sea, lake, or larger stream

Channel

A long, narrow depression eroded by a stream into rock or sediment

Stream banks

Slides of channel

Streambed

Bottom of the channel

Floodplain

Flat valley floor composed of sediment deposited by the stream

Drainage Basins

Also known as a watershed or catchment area

Drainage Basins

Where water from precipitation gathers and flows downhill into a common outlet (river, lake, wetland, ocean)

Drainage Basins

Includes network of streams and rivers that carry water & land surface from which water is collected and directed into those channels

Tributary

Small stream flowing into a larger one

acute angle

Most tributaries join the mainstream at an ______ forming a V or Y pointing downstream

Divide

Ridge or high ground that divides one drainage basin from another

Continental Divide

Separates streams that flow into the Pacific from those that flow into Atlantic and Gulf of Mexico

Dendritic

Drainage pattern resembling the branches of a tree

Radial Pattern

Streams diverge outward like the spokes of a wheel (conical mountains)

Rectangular pattern

Tributaries have frequent 90-degree bends and join other streams at right angles

Trellis pattern

Parallel streams with short tributaries meeting at right angles

Drainage Patterns

Arrangement of streams, rivers, and lakes within a specific drainage basin

Drainage Patterns

Influenced by topography of the land, type of rocks present, and gradient of the terrai

Factors affecting stream erosion and deposition

• Natural Factors

• Human-caused factors

Natural Factors

• Gradient (Steepness) of the streambed

• Precipitation

• Stream discharge

Gradient (Steepness) of the streambed

Slope of streambed affects water flow speed

Steeper gradients

= faster flow = increasing erosive power

Precipitation

Rainfall & snowmelt contribute to water volume in a stream

Higher precipitation rates

= increased water flow & erosive potential

Stream discharge

amount of water flowing through a stream

Stream discharge

is influenced by rainfall, snowmelt, and groundwater contributions, impacting erosive capacity of the stream

Human-caused factors

• Deforestation

• Urbanization

• Damming and channelization

Deforestation

leads to increased erosion due to loss of root systems that stabilise the soil

Urbanization

Construction in urban areas can alter natural drainage patterns, leading to higher runoff rates and increased erosion

Damming and channelization

for flood control or navigation purposes can change flow patterns and sediment transport, impacting erosion downstream

Factors essential for managing and mitigating erosion in streams

• Velocity

• Gradient (slope)

• Channel shape and roughness

• Discharge

Velocity

Maximum ____ near center of channel

Velocity

Higher stream _____ promote erosion and transport of coarser sediments