DELTAS

FOUND AT THE MOUTH OF A RIVER AS IT ENTERS A SEA OR LAKE

WHY DO THEY ONLY FORM AT THE MOUTH OF CERTAIN RIVERS Low energy coast Large sediment load (eg Mississippi) Coastal area with small tidal range and

weak currents. E.g Mediterranean)

Why do we not get deltas in the Bristol Channel?

DESCRIPTION Can be Cuspate (Ebro), Arcuate (Nile) or

birds foot (Mississippi)

Distributarieslagoon

WHY DOES DEPOSITION OCCUR River velocity drops Sediment carrying capacity decreases.

Bedload & suspended load dropped.

Also – seawater and fresh water mixes causing clay particles to coagulate (clump together) – flocculation occurs and settles out of suspension

SEDIMENT BEDS Cross section

Topset beds

Foreset

Bottomset

QUESTION What needs to happen for a delta to

grow in size?

In which seasons will a delta be growing and shrinking?

Why do deltas feature distributaries?