Mass movement

Mudflow

What is Mudflow?

• Mudflow is the movement of top-soil down a gradient in the landscape and happens both gradually and rapidly.

Description of Mudflow

Flows take place gradually, possibly faster at one time in the year than another

Encouraged by wet winters mudflows emerge from the base of a rotational slip and slowly spread and pour over earlier, lower slips and flows into the sea.

Mudflow can travel extremely fast at more than 10ft/s.

How does it happen?

• It is often encouraged by heavy rain and happens most often from October to February when the wet conditions lubricate the protective soil and wash away bits of loose ground gradually. Flash floods can often encourage rapid mudflow, this is also known as a lanslide.

Conditions for mudflowMaterials involved:

• A mixture of mud and water

•Soil and rock

Conditions needed:

•Heavy rainfall for long period of time

•Both gravity and slope angle play a part

•Slope angle must be greater than 10°

Vegetation and human factors:

•There are no human factors

•Soil becomes saturated

Easily saturated top soil

Downslope movement of saturated soil lobe

Angle of slope >10°

Input of precipitation increases weight and lubrication of top soil

Toe marks final resting place

Bowl-shaped hollow marking start of flow

Landslides and Slumps

By James Morrison, Only James.

Type of Mass Movement – Landslides and Slumps

Earliest landslide blocks are hummocky because of glacial erosion and deposition

Key

Downward slumping of heavy basalt rock

Concave sliding surface

Large sections of rock and soil break away and move quickly down-slope as a unit

Processes

A landslide is the movement of large quantities of rock and/ or earth.

Landslides are a form of rotational sliding which is when a mass of rock slumps along a curved plane. This causes the land to break away and move downhill as a unit

This process is very fast.

Conditions

Material involved- • Soft rock – Clay• Hard rock – Sandstone• Soft material such as clay overlies a harder

substance such as sandstone.Weather conditions-• Surface soil is saturated after prolonged heavy

rain which lubricates the rock• Slopes are undercut because of river or sea

erosion• Rock becomes weaker and unsupported.

Conditions Continued

Vegetation-

• Prevented by vegetation as the roots as the roots bind the soil.

• Vegetation also protects the soil from heavy rain

Movement-

• The movement is helped by gravity and this process happens quickly

Slumping

This is defined as occasional, rapid movements of large

quantities of soil and/or rock.

How much slope gives way?

Usually a whole section of a slope gives way when a large amount of unsupported solid rock and/or regolith begins to slip plane.

Regolith – the general name given to the end product of weathering

MovementThe Slump block moves downhill slowly,

Gravity’s Role

• When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs.  The resisting forces helping to maintain slope stability include the slope material's strength and cohesion, the amount of internal friction between grains, and any external support of the slope.  These factors collectively define a slope's shear strength.

Gradient

•   Slope gradient is probably the major cause of mass wasting.   Generally speaking, the steeper the slope, the less stable it is.  Therefore, steep slopes are more likely to experience mass wasting than gentle ones.

WE HAVE GRAFITIED YOUR PRESENTATION!!!!!

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PROCESS

• Definition

Soil creep is the result of repeated expansion and contraction of particles of soil. Heavy rainfall increases the volume of the soil, therefore, weighs it down which makes the soil move downhill under gravity!

Soil Creep is the slowest and least dramatic of all down slope movements. Speed of less than 1mm/year.

Guide Planes!

Easily saturated top soil!

CONDITIONS

• Materials involved:

Large sections of rock and soil.

• Weather Conditions

Rain helps lubrication of the rock.

CONDITIONS CONTINUED

• GRAVITY

The steeper the slope the higher the gravitational force.

The steeper the slope the faster the movement.

CONSEQUENCES

• Tilted trees, damaged walls, Cracked roads

Rock fall

By Lorraine , Heather, Kirsten and Kate

Processes

• Rock fall is the rapid, free-fall of rock from a steep cliff face. Rock fragments fall from the face of the cliff because of the action due to gravity. This is made worse by freeze-thaw action loosening the rock. A scree slope of fallen rock is formed at the bottom of the cliff.

Diagram

Lines of weakness

Free FaceScree accumulates at slope foot forming heaps of sharp debris

Rocks bounce down rather than roll

Conditions

• The ground is vertical and dry to help the process of rock fall to take place. The material that is involved is varying sizes of rock.

• Rock fall usually occurs in colder, wetter climates due to freeze thaw action, one of the main processes, works best at these climates

• Bare, hard rock is very vulnerable to rockfall - water enters the joint, freezes and expands, cracking the rock.

• It is common at high altitudes where there is poor soil and less vegetation.

Mass movement

Rock fall

By Luke, Alexander, David and Gary.

Bare rock, scree slopes and freeze thaw weathering are the three main factors in rock fall

mass movement.

Freeze thaw weathering weakens joints and bedding planes in the cliff. The rock that falls off creates a scree slope. The scree

slope has an angle of repose which is around 30 degrees.

The finer grained scree (talus) fills the small holes in the rocks.

Rockfall mass movement occurs in areas where the temperature is low and

fluctuates around 0 degrees Celsius.

Freeze thaw

Upper part of scree (talus) slope

After gravity has pulled the rock from the rock face it falls down the scree slope, at the bottom of the scree slope small plants

grow and hold the rocks together.

Some plants holding the bottom of the scree slope together

Gravity pulls the rock off the rock face after it has been weakened by freeze thaw.