Part 8Part 8

ALLUVIAL FANS ALLUVIAL FANS and DELTASand DELTAS

• Classic alluvial fan. Fans often develop where confined channels on steep gradients suddenly emerge from their canyons, changing the flow regimen sufficiently to stimulate deposition.

• River deltas are commonly built off a series of anastomotic distributary channels, such as that shown at lower right

• The Mississippi and Atchafalaya Rivers have deposited enormous deltas over the past 6000 years; Delta # 7 being the youngest and #1 the oldest.

• Abandoned distributaries of the Mississippi and Atchafalaya Rivers. The Metairie Ridge distributary channel, separating lower and upper New Orleans, is shown in red

• Until the construction of jetties in the late 1870s, sand bars closed off the mouth of the Mississippi River each year for as much as 3 months at a time following high flows.