Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK
19.3
Look at this satellite image of a landform on the
coast of Japan. Assuming that north is at the
top of the image, in what direction is the long-
shore current flowing? Why is the curve present
at the end of the feature?
Longshore Processes and Depositional Coastlines
Now that we have discussed the basic processes associated with
longshore drift, we can view them in an animated format. To do so,
go to the
Geo Media Library
and access
Longshore Processes
and Depositional Coastlines
. This animation describes the way
that water moves along a shoreline and the landforms that result
from this flow. Watch how oblique-approaching waves cause a
current to develop parallel to the shore. Also see how this current
moves sediment until it reaches bays where it is deposited first to
form spits and then baymouth bars. Most importantly, watch how
the coastal landscape is transformed through time and process.
After you complete the animation, be sure to answer the ques-
tions at the end to test your understanding of this concept.
Like baymouth bars, brackish lagoons form behind barrier
islands that are close to the shore because they are not fully in
contact with the ocean and thus have lower salinity. Once these
lagoons become established, they become the focus of sedi-
ment deposition from three sources: (1) streams flowing off the
mainland, (2) eolian sand blowing landward from the island,
and (3) tides. Taken together, this deposition produces new land
bodies called mudflats (Figure 19.28a), which, if vegetated, be-
come salt marshes (Figure 19.28b). If plant colonization contin-
ues unchecked, due to the lack of strong storms or an outlet to
the ocean, the lagoon is slowly transformed into a continuous
landmass connected to the barrier island.
Stream
Mainland
Stream
Stream
Mainland
Stream
Marsh
Marsh
Mudflats
Mudflats
Barrier islands
Barrier islands
(b)
(a)
Figure 19.28 Infilling of a lagoon.
(a) Because lagoons are water bodies of low energy, they are the focus of sediment deposition, form-
ing mudflats. (b) With time, the lagoon will be transformed into a vegetated salt marsh that connects the mainland with the barrier island.
