Foredune

A foredune is a dune ridge that runs parallel to the shore of an ocean, lake, bay, or estuary. Foredunes consist of sand deposited by wind on a vegetated part of the shore. Foredunes can be classified generally as incipient or established.

Foredunes may begin as shadow dunes that form in the wind shadows of clumps of vegetation. Several shadow dunes may eventually join to form an incipient foredune. When an incipient foredune reaches a height of about 1.5 feet (0.5 m), it has a significant wind shadow of its own. Wind-blown sand will tend to fall on this incipient dune rather than traveling further inland. When a foredune becomes 3 to 5 feet (0.9 to 1.5 m) high, it may trap all of the wind-blown sand from the beach.

In active dune systems, the foredunes appear closest to the sea or other body of water. However, some dune systems, such as those on eroding coasts, do not have foredunes. In those systems, other kinds of dunes may be closest to the water.

A foredune ecosystem begins with the first dune ridge directly behind an active beach. The ridge of a foredune can range in height from a few meters to tens of meters tall. Foredunes are formed when sand accumulates and wind actively transforms the landscape. This results in sand sheets can consuming in-land ecosystems. United States Fish and Wildlife Service actively manages Humboldt Bay’s Lanphere Dunes. Active sand sheets at Lanphere Dunes have been measured to be in excess of six hundred meters.

Parabolic Dunes are identified by vegetated dune ridges and vegetated deflated plains. Due to variable wind gusts, parabolic dunes are commonly unvegetated in troughs or dune swells where wind tunnels transport currents. Ripple alignment in association with the main dunes can also identify parabolic dunes. Ripples minuet accumulations of sand against the main dune swale. The heights of ripples are normally measured on a millimeter to centimeter scale. In Humboldt Bay, the wind is predominately blowing in from the northwest. As a result, the dune ridges are formed parallel to the wind currents while ripples are formed perpendicular to the wind.

Northern California coastal dune environments are subject to high velocity winds at all times throughout the year. This strong variable causes the morphology of the dune ecosystem to constantly change. Dunes can range in height from a meter to tens of meters tall creating elevation changes and habitat complexities. The dune ecosystems surrounding Humboldt Bay, in Humboldt County, California, are classified as parabolic dunes. This is due to the consistent north-northwest winds and dune mat vegetation armoring the arms of the dunes. Invasive species can further armor dune ridges, creating linear dunes, and preventing naturalistic parabolic dunes from being created.

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