|
Spectacular rock formations have developed in coarse, poorly
sorted conglomerates and arkosic sandstones at Hopewell
Rocks in the Bay of Fundy, which has the largest tidal range
in the world. The average gradient of the shore platform
is 3.2°, although it varies because of slight differences
in rock hardness.
Schmidt Rock Test Hammer measurements show that the rock
is generally no more resistant in 16 stacks and in one stack-arch
than in the adjacent platform and cliff. Most stacks, arch-tunnels
and caves in this area result from dissection of the rock
mass along prominent, well-spaced joint planes. Old photographs
suggest that the stacks at Hopewell Rocks may have developed
in the last 100 to 250 years. Notches are ubiquitous at
the cliff foot, and they are responsible for the characteristic
mushroom-shaped appearance of the stacks.
Although there is no consistent relationship between the
depth of notches on the seaward and landward sides of the
stacks, the notches are at higher elevations on the seaward
side. The deepest part of most notches is a little below
the mean high tidal level, although several are up to 1
or 2 m below it, especially on the landward side of stacks.
Stack morphology and notch depth change in a fairly predictable
manner through time, as the stacks become increasingly isolated
from the cliff.
|
