chapter 5.3 mass movements

CHAPTER 5.3 MASS MOVEMENTS“The transfer of rock and soil downslope due to gravity.”

Some types of mass movement are so slow you can’t see them moving.

Year: 2009Year: 2020Year: 2050Year: 2070

CHATER 5.3 MASS MOVEMENTS“The transfer of rock and soil downslope due to gravity.”

Some types of mass movement are very sudden.

Triggers of Mass Movement

Saturation by Water When pores in sediment become filled with water.

Saturation provides a slippery medium upon which the soil particles can slide.

Saturation adds weight to the soil causing it to break loose and slide downslope.

Triggers of Mass Movement

Oversteepened Slopes Slopes that are steeper than about 40 degrees.

Soils can remain stable on slopes up to about 25-40 degrees.

Can be caused by wave action or human construction processes. 40 degree slope

Triggers of Mass Movement

Removal of Vegetation Cutting or replacement of plants that secure the soil.

Plant roots bind soil and regolith together.

Removal of plants removes the “rope” that holds the soil in place.

Triggers of Mass Movement

Earthquakes Rapid movement of tectonic plates.

Can dislodge large amounts of soil at once.

Triggers abrupt and often violent mass movement.

Types of Mass Movements

Geologists classify mass movements based on…

… the kind of material that moves (rocks, mud, snow)… how the material moves(slides, flows, slumps)… the speed of the movement (creep)

Types of Mass Movements

Rockfalls …

• occur when rocks or rock fragments fall freely through the air.

Rockslides …

• occur when a block of material moves suddenly (fast) along a flat, inclined surface.

Types of Mass Movements

Slumps …

• occur when material moves downward along a curved surface. • leave a crescent shaped cliff just above the slump.

Flows …

• occur when material containing a large amount of water move downslope as a thick fluid• “mudflows” move quickly• “earthflows” move slowly

Types of Mass Movements

Creeps …

Types of Mass Movements

• moves only a few millimeters or centimeters per year.• affected by freezing and thawing• cannot be observed directly as it happens (too slow)

A

B

1 mm

Creeps …

Types of Mass Movements

HSW: Geography Basics: Five Ways Lands Change

Sideling Hill

Assignment:

Read pgs 148-149.Answer the questions under “ASSESSMENT” on pg 149.

DO NOT do Question 5(c).