Jasper Beach, Machiasport, Maine
Jasper Beach is located in Howard Cove, Machiasport, just west of
Machias Bay (Figure 1). It is a dominantly gravel beach, about 800 m long,
and oriented East-West (Timson, 1981). Bedrock frames Howard Cove, making
Jasper a pocket beach. It is also a barrier spit that originates at an
eroding bluff of glacial material on the west and terminates at a tidal
inlet on the east. In addition to the bluff, the beach is backed by fresh
and saltwater lagoons and a salt marsh (Figure 2). Jasper Beach is operated
as a Town Park by Machiasport and is located on Rt. 92, beneath the
abandoned Distant Early Warning Station radar facility on Howard Mountain.
Limited parking space is provided.
The local bedrock is a complicated mix of volcanic rocks within the
Eastport (Osberg et al., 1985) or Leighton Formations (Gates and Moench,
1981). The rocks are highly fractured and easily eroded by waves. At the
eastern end of the beach, several sea caves and sea arches have formed in
the bedrock and collapsed in the past 15 years.
Although Jasper Beach is named after the red volcanic stone that is
common on the beach, that rock is not truly jasper. Jasper is a form of
silica that is enriched in iron, whereas the red stone on Jasper Beach is a
fine-grained volcanic rock called rhyolite. Its attractive appearance is
also due to the polished surface formed by constant abrasion against sand
grains.
Figure 3 |
Glacial deposits cover much of the area surrounding Jasper Beach.
Till underlies the beach and crops out on the landward side of the lagoon
(Thompson and Borns, 1985). The 10 m high bluff on the western end of the
beach is a stratified sand and gravel deposit that is apparently
glacial-fluvial outwash (Figure 3). Clasts within the deposit are mostly
volcanic rocks with assorted quartzites and granitic clasts. |
Although local bedrock is eroding, the bluff appears to supply most
new sediment for the beach. Boulder and cobble-size clasts are common
here, and beach sediment becomes finer grained away from the bluff because
of either selective longshore transport of smaller clasts or because of
clast abrasion and comminution toward the east. At the eastern end of the
beach, well-sorted, coarse sand is common.
Figure 4 |
Several steps, or storm berms, are typically visible at low tide on
the beach (Figure 4). These are complex erosional and depositional
features formed during storms when water level is elevated above its
average position. Cusps, or regularly spaced curved indentations in the
beach, are common along all of the berms, although the spacing between
cusps is different at different heights. |
Figure 5 |
The size and shape of the beach sediment becomes generally finer
grained from the highest storm berm to the low-tide line. Within cusps
there are also changes in the size and shape of clasts. Large, disc-shaped
stones collect on the top of the cusp while better rounded, "rollers"
tumble to the bottom of the cusp (Figure 5). The disc-shaped clasts are of
volcanic rock while the rounder stones are granites and quartzites. |
Figure 6 |
About halfway down the beach from the eroding bluff, the size of
the upper beach sediment becomes fine-grained enough to trap sufficient
water for dune plants to survive (Figure 6). The dunes here are not like
"sand" dunes in southern Maine because most of the sediment is brought to
the top of the beach by storm waves, not by the wind. Large logs are also
commonly found in the dune area. American Beach Grass (Ammophila
breviligulata), the common dune plant in southern Maine, is observed here,
but Beach Pea (Lathrus japonicus) is unusually abundant. |
Figure 7 |
At the eastern end of the beach, large flood and ebb-tidal deltas
occur on the ocean and lagoon sides of the tidal inlet, respectively
(Figure 7). These form in response to deposition of sediment as tidal
currents slow upon entering the ocean on ebb tides and the lagoon on flood
tides. Waves also influence the ebb tidal delta, and wave-formed swash
bars are usually visible at low tide. These are driven onto the beach by
waves over a period of months. It is interesting to observe that at low
tide, the tidal inlet water disappears into the coarse sand of the tidal
delta. |
Figure 8 |
As sea-level has risen during the past few thousand years, Jasper
Beach has been driven more and more into Howard Cove. Evidence for the
landward migration of the beach is seen in the burial of shrubs and trees
by beach sediment on the landward side of the beach. At low tide, on the
seaward side of the beach, preserved terrestrial environments emerge from
burial by the beach for millennia (Figure 8). Here, remnants of beach
gravel lie above salt marsh peat and a forest rooted in glacial till. The
dense nature of the salt marsh peat is a mark of how heavy the weight of
the beach was as it passed over this former wetland. |
Figure 9 |
Cores through the salt marsh and lagoon (Figure 9) allow us to
depict a cross section of the overall geology of the beach. Till provides a
foundation for the marine deposits, and is slowly being drowned on the
landward side of the lagoon by salt marsh. The marsh exists at mean high
water today and rises several millimeters per year in response to sea-level
rise. The lagoon is slowly rising over the
marsh peats and is, in turn, being overridden by the landward-migrating
beach. Radiocarbon dates from the bottoms of cores in these environments
demonstrate that thousands of years are required for the beach to move
landward. Based on this, we might estimate that the material cropping out
today on the beach is considerably more than 4,000 years old. |
References Cited
Gates, O., and Moench, R. H., 1981, Bimodal Silurian and lower Devonian
volcanic rock assemblages in the Machias-Eastport area, Maine: U.S.
Geological Survey, Professional Paper 1184, 23 p.
Gehrels, W. R., and Belknap, D. F., 1993, Neotectonic history of eastern
Maine evaluated from historic sea-level data and C-14 dates on salt marsh
peats: Geology, v. 21, p. 615-618.
Osberg, P. H., Hussey, A. M., II, and Boone, G. M., 1985, Bedrock geologic map of Maine:
Maine Geological Survey, Map, scale 1:500,000.
Timson, B. S., 1981, Jasper Beach, Machiasport, Maine: Its significance as a
gravel spit and relevance to the Critical Areas Program: Maine State
Planning Office, Critical Areas Program, Planning Report 75, 30 p.
Thompson, W. B., and Borns, H. W., Jr., 1985, Surficial geologic map of Maine: Maine
Geological Survey, map, scale 1:500,000.
Web text and photos by Joe Kelley
Originally published on the web as the June 2000 Site of the Month.
Last updated on August 3, 2006
