gravitational tectonics
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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
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