Lesson 10

Geological Hazards

Geological Hazard

An adverse geological condition capable of causing damage to life and property.

Mass Wasting

The downslope movement of rock, soil, and debris due to gravity without the need for a transporting medium.

Mass Wasting Triggers

Saturation of soil with water, Removal of vegetation, Earthquakes, Human activities such as mining or road construction

Mass Wasting Factors

Angle of Repose and Liquefaction

Angle of repose

The steepest angle at which a material remains stable

Liquefaction

happens when a water-saturated surface material loses strength and behaves like a fluid that flows

Flow Movement

Movement of soil, rock, and water like a fluid.

Earthflow

leaves a scar on the slope of a hillside (forms a tongue or a teardrop)

Debris flow

rapid flow of soil and regolith containing a large amount of water

Mudflow

movement of fine-grained soil

Lahar

movement of volcanic material

Fall Movement

Free-fall movement of rock or debris from steep slopes

Talus slope

cone-shaped, fall to the base of the cliff (rock fragments)

Rockfall

sheets of rock that has fallen freely from a cliff face

Avalanche

snow, rock or debris that hurtle downslope at speeds exceeding 200kph

Slide Movement

Downslope movement of material along a weak surface.

Landslide

sliding of rock, debris, and soil (type of slide movement)

Mudslide

sliding of mud

Rockslide

sliding of rocks on a planer surface

Slump

sliding of rock masses or unconsolidated material on a curved surface

Landslide

The mass movement of rock, soil, and debris down a slope due to gravity (separate definition)

impending landslide

Earlier landslide, Tension Cracks, Things Moving, and Water doing something, are different are signs of _________

Tension cracks

stress and friction in rocks/soil cause __________

Rapid movement

The rate of movement for Slump, Debris flow, Earthflow, Avalanche, Landslide, and Rockslide

Slow movement

The rate of movement for Creep and Solifluction

Solifluction

Occurs when water cannot escape from saturated surface

Landslide Mitigation

Actions taken to prevent or reduce the risk to life, property, social and economic activities, and natural resources from landslides

Sinkholes

Topographic depression created when groundwater dissolves the underlying limestone bedrock/Large deposits of limestone, carbonate rock, and salt beds exposed to circulating ground water

Cover collapse

A sinkhole that occurs when the covering sediments contain a significant amount of clay. Over time, surface drainage, erosion, and deposition of sinkhole into a shallower bowl of depression

Cover subsidence

A sinkhole where the sediment covers are permeable and contain sand and small surface depressions

Dissolution

A sinkhole that occurs when raining where limestone is exposed at land surface or also is covered by thin layers of soil and permeable sand

Artificial Sinkhole

Sinkhole caused by human activities such as construction, groundwater extraction, etc.

PHIVOLCS

Philippine Institute of Volcanology and Seismology