Meanders and Oxbow Lakes
Deltas and Alluvial Fans
Chapter 10
Earth Science
Meanders
• As a river reaches a
base level, it slows
down and deposits
sediment
• The valley fills up
and the river tends to
meander (zig-zag)
cutting into the valley
walls and widening
the valley floor
Meanders
• The river channel is the deepest and quickest on
the outside of the curves, hence erosion
• The river channel is shallowest and slowest on
the inside of the curves, hence deposition
(point/sand bar)
Oxbow Lakes
• Sometimes, usually during floods, the river will
jump the channel leaving a meander or loop out
• This eventually becomes an oxbow lake
• Meander scar = dried up oxbow lake
Depositing Sediment
• Rivers deposit sediment because of energy loss
due to:
▫ 1. Decrease in speed – due to a decrease in slope
or bed widening
▫ 2. Decrease in discharge (volume) – because of
water loss due to
 A) Irrigation
 B) Evaporation
Deltas
• Deltas form when a river flows into a quiet body
of water (i.e. lake, sea)
Deltas
• The first sediment deposited at the mouth of the
river is the bedload (rock, gravel, coarse sand),
then suspended material (fine sand, silt, clay).
• Solution stays in solution, hence salt water
Deltas
• Deltas do not form where rivers flow into the
• A) Open ocean where there is strong wave action
to take the sediment away
Deltas
• Deltas do not form where rivers flow into the
• B) Ocean where the continental shelf ends close
to shore
Alluvial Fans
• 1. Form on land
• 2. Consist of coarse
sediments (gravel,
sand)
• 3. Are steep (10 ft.
slope)