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Earth Science Notes2 Q2: Water, Anchoring Effects of Plant Roots

The document discusses mass wasting, which is the downslope movement of soil, rock, and regolith under the influence of gravity. It identifies four main factors that influence mass wasting: slope angle, the role of water, the presence of troublesome earth materials like expansive soils, and the presence of weak materials and structures. The document also describes different types of mass wasting processes like slope failures, sediment flows, solifluction, debris flows, mud flows, creep, grain flow, and debris avalanches. Finally, it lists events that can trigger mass wasting like earthquakes, slope modification, undercutting, changes in hydrologic or slope characteristics, and volcanic eruptions.

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Finli Isidore Cabahug
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55 views3 pages

Earth Science Notes2 Q2: Water, Anchoring Effects of Plant Roots

The document discusses mass wasting, which is the downslope movement of soil, rock, and regolith under the influence of gravity. It identifies four main factors that influence mass wasting: slope angle, the role of water, the presence of troublesome earth materials like expansive soils, and the presence of weak materials and structures. The document also describes different types of mass wasting processes like slope failures, sediment flows, solifluction, debris flows, mud flows, creep, grain flow, and debris avalanches. Finally, it lists events that can trigger mass wasting like earthquakes, slope modification, undercutting, changes in hydrologic or slope characteristics, and volcanic eruptions.

Uploaded by

Finli Isidore Cabahug
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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EARTH SCIENCE NOTES2 Q2

 Mass Wasting

= Downslope movement of soil, rock, regolith (region of loose unconsolidated rock and dust that sits
atop a layer of bedrock.)

= Under the direct influence of gravity.

WHAT INFLUENCES MASS WASTING?

1. Slope Angle

= On a steep slope, the slope-parallel component increases while the slope-perpendicular component
decreases. Thus the tendency to slide down the slope becomes greater.

= All forces resisting movement downslope can be grouped under the term shear strength which is
controlled by factors such as frictional resistance and cohesion of particles in an object, pore pressure of
water, anchoring effects of plant roots.

2. Role of Water

= Water has the ability to change the angle of repose (the steepest slope at which a pile of
unconsolidated grains remain stable).

= Water can reduce the friction along a sliding surface.

3. Presence of Troublesome Earth Materials


 Expansive and hydro compacting soils

= Contain a high proportion of smectite or montmorillonite which expand when wet and shrink when
they dry out.

 Sensitive Soils

= Clays in some soils rearrange themselves after dissolution of salts in the pore spaces.

= Clay minerals line up with one another and the pore space is reduced.

 Quick Clays

= Water-saturated clays that spontaneously liquefies when disturbed.

4. Weak materials and structures


= Become slippage surfaces if weight is added or support is removed (bedding planes, weak layers, joints
and fractures, foliation planes.)

DIFFERENT PROCESSES OF MASS WASTING (2)

 Slope Failures

= Sudden failure of slope resulting in transport of debris downhill by rolling, sliding, and slumping.

 Sediment Flow

= Materials flow downhill mixed with water or air;

= Slurry and granular flows are further subdivided based on velocity at which flow occurs.

Slurry Flow = Solifluction, Debris Flow, Mud flow

Granular Flow = Creep, Grain Flow, Debris Avalanche

o Solifluction

= is a geomorphic process that involves the slow movement of water-saturated soil down a slope and
usually occurs on frozen subsoil or during freeze-thaw activity.

o Debris Flow

= are defined as mass‐wasting events in which turbulence occurs throughout the mass. Varieties of
these are called earthflows, mudflows, and debris avalanches.
o Mud Flow

= is a liquidy mass of soil, rock debris, and water that moves quickly down a well ‐defined channel.

Creep
= A slow, gradual movement of soil or regolith downhill over time.
= Vegetation helps reduce the rate of soil creep.
Grain Flow
= is a type of sediment-gravity flow in which the fluid can be either air or water, acts only as a lubricant, and
grains within the flow remain in suspension due to grain-to-grain collisions that generate a dispersive pressure
to prevent further settling.

Debris Avalanche
= Rapidly churning mass of rock debris, soil, water, and air that races down very steep slopes.
EVENTS THAT TRIGGER MASS WASTING PROCESSES

 Shocks and vibrations

= Earthquakes and minor shocks such as those produced by heavy trucks on the road, man-made
explosions

 Slope modification

= Creating artificially steep slope so it is no longer at the angle of repose.

 Undercutting

= Due to streams eroding banks or surf action undercutting a slope.

 Changes in hydrologic characteristics

= Heavy rains lead to water-saturated regolith increasing its weight, reducing grain to grain contact and
angle of repose;

 Changes in slope strength

= Weathering weakens the rock and leads to slope failure;

= Vegetation holds soil in place and slows the influx of water;

= Tree roots strengthen slope by holding the ground together.

 Volcanic Eruptions

= Produce shocks;

= May produce large volumes of water from melting of glaciers during eruption, resulting to mudflows
and debris flows.

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