A tiny bit of the sand on the beaches comes
from the eroding sea cliffs, but the vast vast
majority of the sand on the beaches in washed into
the sea from rivers.
Mountains and hills are eroded by wind and
water and all the bits of rock -- from tiny
clay particles to sand to big boulders -- ends up
in the rivers. The rivers break up the boulders
into more and sand and clay and carry all these
small rock pieces out into the ocean. The clay
gets washed out into the deep water, but the
sand-sized pieces are heavy enough, that they fall
down to the bottom as soon as the rivers enter the
Ocean currents called long-shore
currents carry the sand away from the mouth of
the river and down the shore. In California, the
long-shore currents move southwards.
Sometimes you can notice them when you swim in the
ocean. You will find that you are drifting away
from the spot you entered the water. The sand is
moving in the same direction, but we don't usually
A really good 20-minute movie on this subject
is called "Beach, River of Sand". Your school
district may own a copy you could borrow.
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