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Rocks

Sedimentary Rocks - Weathering and Erosion.

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.

Weathering breaks a rock down into small pieces.
The two main processes are exfoliation and freeze-thaw weathering.

Exfoliation occurs when rocks are heated and expand in the heat of the day
and then cool and contract in the cold of night.
Thin slithers of rock tend to flake off the surface,
and these can then be broken further into tiny pieces.
Think of exfoliation as flaking.

Freeze-thaw 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.

Erosion is a slow process of wearing away weathered rock
by action of the wind, rivers and waves.

What happens to the small pieces of rock after weathering and erosion?

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