Sedimentary Rocks - What is Weathering and Erosion?
Where do Sediments Come From?
Sediments have come from the weathering and erosion of
surface rocks. The original surface rocks were igneous rocks
formed from the cooling of molten magma.
Surface rocks today are igneous, sedimentary or metamorphic.
What is Weathering?
Weathering breaks a
rock down into small pieces.
The two main processes are exfoliation and freeze-thaw weathering.
What is Exfoliation?
Exfoliation occurs when rocks are heated and
expand in the
heat of the day and then cool and contract in the cold of night.
The expansion and contraction makes thin slithers of rock
tend to flake off the surface, and these flakes can then be
broken further into tiny pieces. Think of exfoliation as flaking.
What is Freeze-Thaw Weathering?
weathering occurs when water
gets into cracks in rock
and then freezes (below 0 °C) in cold weather.
Water expands when it freezes and turns to ice,
and the expansion can cause the rock to split and fragment.
In warmer weather (above 0 °C) the ice melts (called thawing),
and new cracks are exposed allowing the process to repeat itself.
What is Erosion?
Erosion is a slow
process of wearing away
by the action of the wind, rivers and waves.
All rocks would have been worn down flat to sea level long ago
if hills and mountains were not constantly being
formed by the movement of plate tectonics. See the rock cycle.
What happens to the
small pieces of rock after weathering and erosion?
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