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WEATHERING and the BREAKDOWN of ROCKS. WEATHERING. The process by which rocks and minerals break down at or near the surface of the Earth. EROSION. The process by which moving water, wind, ice or gravity carries away pieces of rock and deposits it elsewhere. - PowerPoint PPT Presentation
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GE 141 Grades Exam 1
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WEATHERING
EROSION
WEATHERING and the BREAKDOWN of ROCKS
The process by which rocks and minerals break downat or near the surface of the Earth.
The process by which moving water, wind, ice orgravity carries away pieces of rock and deposits it elsewhere.
WEATHERING and EROSION are inter-related.WEATHERING speeds EROSION.
WEATHERING PROCESSES
MECHANICAL WEATHERING
WEATHERING and the BREAKDOWN of ROCKS
MECHANICAL WEATHERING breaks a mineralor rock into smaller pieces but does not changethe chemical make-up of the pieces.
Turns big rocks into little rocks.
Mechanical Weathering increases the surface area thatcan later be chemically weathered.
FROST WEDGING
WEATHERING and the BREAKDOWN of ROCKS
Water expands when frozen.Expands ~ 9%.Water trapped in cracks
freezes and expands.Actively fractures the rock.Works best where temperatures
fluctuate above and below0C (32F).
When water melts, it seepsdeeper into the crack andthen refreezes.
FROST WEDGING
WEATHERING and the BREAKDOWN of ROCKS
Breaks off blocks or slabs of rock.Broken pieces fall downslope.Accumulate as TALUS.
FROST WEDGING
FROST HEAVES AND POTHOLES
WEATHERING and the BREAKDOWN of ROCKS
CRYSTAL GROWTH
Salt water, usually from the ocean, gets into fractures.When it evaporates, crystals grow that expand.Expansion of crystals breaks the rock.
Before
After
Cleopatra’s NeedleCentral Park, NY
WEATHERING and the BREAKDOWN of ROCKS
THERMAL EXPANSION and CONTRACTION
Heat causes external layers of rock to expand.Mineral expand at different rates.Quartz expands more than feldspar.Those minerals that expand more, exert pressure on
those that expand less.Generally affects only the surface layer of a rock.
(Rock is a poor conductor of heat)
Forest FireHigh alternation of temperatures (deserts)Water or moisture speeds the process.
WEATHERING and the BREAKDOWN of ROCKS
MECHANICAL EXFOLIATION
When overlying mass of rock and sediment is released,pressure on the underlying rock is released.
Allows the rock to expand.Expansion takes place outward
from the exposed surface.Sheets of rock will fall off.
WEATHERING and the BREAKDOWN of ROCKS
MECHANICAL EXFOLIATION
WEATHERING and the BREAKDOWN of ROCKS
MECHANICAL WEATHERINGOTHER TYPES
ROOT WEDGING
Trees grow in cracks in rocks and the force related toexpansion with growth breaks the rocks.
WEATHERING and the BREAKDOWN of ROCKS
MECHANICAL WEATHERINGOTHER TYPES
ABRASION
Contact of weathered and eroded particles with otherrock during erosion also leads to mechanicalbreakage due to ABRASION.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
Causes a change in the chemical composition of rocksand minerals being affected.
Attacks rocks and minerals that are unstable at theEarth’s surface first.
Produces stable byproducts.Minerals that are stable at the Earth’s surface are less
affected by chemical weathering.Most change takes place through contact with water.Water carries ions from place to place
participates in the reaction itselfcarries away the products = erosion.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
Chemical weathering occurs faster when weatheredmaterial is broken up first by mechanicalweathering.
Increased surface area allows chemical weatheringto occur at a faster rate.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERINGDISSOLUTION
Water removes ions or ion groups from a rock ormineral and carries them away.
Precipitate later when water evaporates.Due to the bipolar nature of water molecules,
ions become dissolved and are transported insolution.
WEATHERING and the BREAKDOWN of ROCKS
