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The Straight Shore,
northeast Newfoundland
Evidence from the sandy coasts of the
Straight Shore (the coast between Cape Freels and
Bonavista Bay - see papers B17, B21) shows how a
coast can change behaviour in response to changes
in rates of sea-level rise. Rising sea level
reached -0.7 m 3000 years ago, and attained the
modern level 2000 years ago. At Deadman's Bay,
the beach had been slowly migrating with rising
sea level before 2000 BP. During storms, sediment
was transported to the rear of the beach in
overwash channels and flood deltas. After 2000 BP
all this activity ceased: the washover channels
became inactive, and flood deltas became peat
covered.
Farther north, a large dune foreland had
accumulated at Man Point prior to 3000 years ago.
As sea-level stopped rising, the dune ridges were
slowly buried in peat. Today, perhaps in response
to rising sea level, the foreland is being eroded
(see photograph) and sand is being tranported
farther north. A stroll along the beach reveals a
cross-section through the ancient dune ridges
that lie below woody peat up to 3 m thick.
Indurated
dune ridges overlain by peat at Man Point,
Newfoundland
St. George's
Bay, Newfoundland
In publications B8
and B12 we have described the evolution of the
coast here. The 12 km-long Flat Island spit is
composed of gravel beach ridges with a veneer of
dune sand in places. The sources of the gravel
are the eroding coastal bluffs that extend 40 km
to the southwest. The gravel is moved in the
swash zone, and the sand appears to move along
the coast independently, in nearshore bars.
Radiocarbon dates on the spit extend back to 1350
years BP, but other evidence suggests that this
spit, and the beach-ridge plain at nearby
Stephenville, formed during the past 3000 years,
a period of continued slow sea-level rise. The
oldest beach ridges lie below the limit of the
modern high tides, and salt marshes are spreading
along the depressions between beach ridges as sea
level continues its slow rise.
Flat Island Spit, St. George's
Bay. The spit is 12 km long.
The spit lies on
the flank of a deep basin, and in order to
prograde along the coast, it formed the
underwater barrier platform shown in this seismic
record. Multibeam mapping (papers B22 and B23)
reveal the morphology of the platform in detail.
Seismic section through beach
ridge complex at Stephenville. The oldest
radiocarbon date on the beach ridge plain is 2640
BP.
East
Point, Prince Edward Island
At the eastern end of Prince
Edward Island the north-facing coast is
retreating whereas the southeast-facing coast is
stable or prograding. We hypothesized that
Milne Bank, a shallow submarine bank located at
the junction of the two coasts, was formed by
deposition of sand eroded from the north coast,
and that sand was moved from Milne Bank onto the
southeast coast. To test this hypothesis Milne
Bank was mapped in 1997 and 1999 with multibeam
bathymetry mapping systems. A repeat survey
of the sea floor was conducted in one area.
We showed that sand waves are
migrating to the south at 17 m/yr on Milne Bank
(see images below). Sand from the eroding north
coast enters Milne Bank and is carried in sand
waves to the prograding end of the bank;
however, some sand is re-circulated northward,
reaching as far as tha large arcuate sand wave
that marks the northern edge of Milne bank.
The lack of an obvious sediment pathway from the
bank to the southeast coast suggests that Milne
Bank is a major sediment sink, rather than a link
between the two coasts. This work is
described in publication B31.
Milne Bank, a
large sand bank just offshore from East Point,
PEI. The box outlines the area of repeat surveys.
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