North
Padre Island is a north-trending barrier island that is
about 2000 years old. On the Gulf side
of North Padre Island sediment is deposited by longshore currents,
resulting in
seaward progradation of the barrier island.
This beach sand along the Gulf side of the barrier island is blown by
winds landward resulting in the development of a vegetated foredune
ridge up to
5 meters high. Storm surges commonly
breach this foredune ridge resulting in washover fans which deposit
sand on the
other side of these ridges and even into the Laguna Madre on the west
side of
the island, resulting in landward progradation of the barrier island
into the
lagoon. Vegetated barrier flats extend
westward from the foredune ridges to Laguna Madre. Active dune fields
are
scattered across the vegetated aeolian flats. These active dune fields
are
migrating to the northwest due to prevailing winds from the southeast.
There are
presently large lobes of sand that can be seen in Laguna Madre that
appear to
have prograded westward out into the lagoon.
The origin of this sand is problematic.
Wind, water, and tides are all factors that contribute to the
deposition
of these fan-like features. These lobes
of sand are mixtures of wind-blown sand and sand deposited by washover
fans
from the Gulf side of the island and Aeolian sand washed in from the
center of
the island. By examining the sediment composition and grain size, the
proportion of aeolian and washover sand in these fan-like lobes can be
determined. This will allow for a more
complete understanding of the mechanisms of landward progradation of
barrier
islands.