GRAVITATIONAL

TECTONICS

INDEX

o Landslides

o Slumps

o Olistostrome

o Normal faults and thrusts

LANDSLIDES

o Landslides are rocks, earth or debris flows on slopes due to

gravity.

o They are also known as mud flows, debris flows, earth

failures, slope failures, etc.

o They can occur on any

terrain given the right

conditions of soil, moisture

and the angle of slope.

o They can be triggered by:

Rains

Floods

Earthquakes

Human-made causes:

grading, terrain cutting

and filling, excessive

development...

FACTORS There are three main factors that

control the type and rate of mass wasting that might occur at the Earth's surface:

o Slope gradient: the steeper the slope of the land, the more likely that mass wasting will occur.

o Slope consolidation: sediments and fractured or poorly cemented rocks and sediments are weak, they are more prone to mass wasting.

o Water: if slope materials are saturated with water, they may lose cohesion and flow easily.

TYPES o Falls - rocks fall or bounce

through the air

o Slides - rock and/or

sediment slides along

Earth's surface

o Flows - sediment flows

across Earth's surface

SLUMPS

o A slump is a mass movement process of slope failure, in which

a mass of rock or unconsolidated material drops along a

concave slip surface.

o Slump units move downslope as an intact block (without

internal deformation of the landslide material) and frequently

rotate backwards.

o Slumps are sometimes caused by:

Clear cutting on unstable soils Floods.

Sagging and rotational movement of the mass of soil.

Water infiltration and lubrication of clay-rich soils

below.

SUBMARINE SLUMP

o It’s caused in a submarine canyon or on a continental slope,

relatively rapid and sporadic downslope composed of sediment

and organic debris that has built up slowly into an unstable or

marginally stable mass.

o A slumping episode may trigger other slumps farther down

the canyon or may create turbid, dense slurries of water and

sediment, which flow downslope as turbidity currents.

OLISTOSTROME

o The term olistostrome is derived from olio - a dish of many ingredients or stew; a mixture of heterogeneous elements. And stroma- a bed covering (Greek equivalent of the Latin stratum).

o An olistostrome is a sedimentary rock formation that comprises a chaotic assemblage of blocks of preexisting rocks, which can be of considerable size, in a finer grained matrix.

o Olistostromes are the result of submarine slumping or gravity sliding on an unstable shelf.

NORMAL FAULTS AND THRUST

o Some scientists argue about the role of gravity in the

formation of normal faults and thrusts.

o It would very difficult to push a thin sheet of rock very far

horizontally without breaking it up because its internal

strenght is too low.

o The magnitude of shear stress necessary to move a mass of

rock would be greatly reduced if the base of the mass were

under high pore-fluid pressure. Because of that, they

maintained that gravity is necessary to move a thrust

sheet.

o (Pore fluids are fluids that occupy pore spaces in a soil or

rock. It can indicate the degree of consolidation of an

earthwork, zero pressure indicating complete consolidation)

BIBLIOGRAPHY

Web Pages:

o http://www.ussartf.org/landslides.htm

o http://bio-geo-terms.blogspot.com/2006/06/slump.html

o http://www.britannica.com/EBchecked/topic/570879/submarine-slump

o http://www.geologyrocks.co.uk/glossary/olistostrome

Books:

o Hatcher, 1995. Structural Geology (pg. 220, 225)

o Twiss and Moores, 1992. Structural Geology (pg. 440)

THE END LÓPEZ

GUAL