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The Variety of Maine's Changing Shoreline
|Maine is famous for its "rockbound coast" buttressed by rugged, unchanging
cliffs of stone. Rocky points such as Portland Head,
photographed a century ago, show little change after a hundred years of
storms (Figure 1). This is because Maine's bedrock is very strong and consolidated,
hence it resists erosion from waves and weather.
|Other parts of Maine, however, have a "soft coast" of loose or unconsolidated
materials that are subject to erosion. A landslide this year in Argyle,
Maine (Figure 2), illustrates that shoreline changes are ongoing. Although
a slow, steady rise in sea-level is the underlying reason for erosion along
the coast, the most noticeable erosion occurs quickly during individual
storms or landslide events.
A vivid example of profound shoreline change occurred during a large
landslide in Rockland in April,
1996. Photographs taken during the course of the event, which lasted
for several days, document the geologically rapid retreat of the bluff
through two houses (Figure 3). The movement of a large mass of material
onto the tidal flat extended the shoreline seaward for a time (Figure 4),
but the sea immediately began to erode the landslide material from the
tidal flat. People began trying to stabilize the
landslide mass (Figure 5). The building debris was removed, and the
surface of the landslide was graded and planted with grass. Waves have
continued to erode the outer area, but there are plans to contain the landslide
deposit by engineering its seaward edge.
|In other locations along Maine's "soft coast" where the bluffs are clearly
eroding, some property owners have taken measures to prevent damage to
their buildings. One such place is a stretch of the Jonesport coast where
the land is underlain by peat bogs and Ice Age mud. These materials succumb
easily to wave attack. As the bluff has eroded through the years, some
houses in the area have been moved back from the edge. Unfortunately, coastal
roads limit the places to which many of the dwellings can be moved. For
other properties, the owners have tried to protect buildings by forestalling
bluff erosion (Figure 6). Over the long run, this strategy can prove to
be expensive, in some cases exceeding the value of the structure being
protected. In addition, for regions with rising sea level, attempts to
"permanently" fix the shoreline position with a wall will cause unintended
problems such as eliminating the intertidal clam flats or salt marshes
in the adjacent areas.
|Beaches make up another part of the "soft coast."
They respond to rising
sea level by eroding or by moving landward. Sometimes, during large
storms, the breaking waves cut an erosional notch in the lower part of
the beach (Figure 7). Normally these erosional notches heal by the following
summer as smaller waves wash sand back onto the beach. In the early spring
of 1997, erosion of the beach at Reid State Park uncovered buried
rockets from World War II. During the summer, they were again covered
by sand. In November and early December, after fall storms had eroded the
beach again, the rockets were removed in a cleanup
effort. By mid-December, sand had moved back onto the beach again,
burying the cleanup area beneath two feet of sand. In this example, careful
measurements demonstrated the movement of sand on the beach. Where beaches
are undeveloped or have not been carefully surveyed, however, it is more
difficult to see how the beach changes from one time to another. Summer
visitors may see the same image of the beach year after year, not knowing
that dramatic changes have occurred during the rest of the year.
|Beaches with artificial structures cannot respond so easily to natural
forces because the presence of buildings in the sand dunes, or seaward
of them, inhibits the beach from adjusting to storms and rising sea level.
Many houses in Maine built too close to the shore have been claimed by
the sea during winter storms (Figure 8), and many more properties are at
risk to changes in the shoreline position. For this reason, the State of
Maine does not allow new buildings to be located in frontal dune settings,
and discourages enlargement of existing structures in this dynamic environment.
Web text by Joe Kelley.
Originally published on the web as the July 1999 Site of the Month.
Last updated on October 6, 2005