Download Sediments

SEDIMENTS
What are sediments?
As ocean waves crash against rocky cliffs, bits and pieces
of rock break off. The larger pieces form pebbles and
boulders; the smaller bits form sand.
Some of the pieces of rock are carried out to sea and settle on
the ocean bottom. Others are washed up onto land to form
beaches. The sand, pebbles and boulders are examples of
Sediments.
Sediments are materials that have settled from water or air.
The materials that make up sediments include pieces of rock
and the remains of animals and plants.
HOW DO SEDIMENTS
FORM?
Most sediments are made of rock. The breakdown of rock
into sediments is called weathering. As rocks are exposed
to the weather, they are slowly broken down by the action
of wind and water. Rocks can break apart into small bits and
pieces or be changed into new materials.
The breakup of rock into pieces is called mechanical weathering.
Water causes most mechanical weathering. For example,
mountain streams flowing over rock gradually wear the rock
away.
Water trapped in cracks in a rock can freeze and cause cracks
to become larger. When the cracks get big enough, the rock
eventually splits up into smaller pieces.
Water can also combine with rock to change the rock into
New materials. Clays used for modeling and making pottery
are formed by water combining with certain kinds of
rock. The changing of rock into new material is called
Chemical weathering.
Although most weathering is caused by the action of water,
the wind also wears away rock. As the wind blows, it carries
sediments. If the sediments are blown up against a rocky cliff,
the scouring action of the sand hitting the rock causes
mechanical weathering. In dry areas such as deserts, the wind
creates large amounts of sediments.
Sediments are also made of plant and animal remains. When
a plant dies, its roots, stems, and leaves rot on the ground.
The rotting plant parts break up into bits and pieces. In swamps
and marshes, rotting plant remains can pile up several feet thick
over hundreds of years.
HOW DO
SEDIMENTS
MOVE?
Erosion
The carrying away of sediments is called erosion. Most sediments
are moved by running water in streams and rivers.
As the water in a stream or river flows downstream, it carries
different-sized sediments. The heavier sediments-boulders,
sand, and gravel-are slowly pushed along the bottom of the
riverbed. REMEMBER BOULDERS, PEBBLE, GRAVEL, SAND,
SILT AND CLAY-SEDIMENT SIZE FROM LARGE TO SMALL.
Lighter sediments, including plant remains, silt, and clay,
float in the moving water. The floating sediments are
suspended in the water. The mixture of water and floating
sediments is called a suspension. In deep places of the river
where the water slows down, the suspended sediments
slowly start to sink and eventually settle to the bottom.