Geoscience Reference
In-Depth Information
Fig. 4.13
Raised beds of
cockles on a hill at Point Samson,
northwest Western Australia.
These shells extend 15 m above
sea level. In this region, the
paleo-tsunami flowed up the
valley and over the hills in the
background. The minimum age
for the event, based on
radiocarbon dating of the shells,
is AD 1080
Fig. 4.14
Chiseled boulders
deposited in bedded gravels in a
mega-ripple about 5 km inland of
the coast at Point Samson,
northwest Western Australia. The
dip in bedding aligns with
bedrock-sculptured features in
the area (Fig.
4.15
) and shows
flow from the northwest in the
Indian Ocean
waves overrode hills 60 m high, another 1 km inland,
carving wind gaps 20 m deep through ridges. Sand and
gravel were then deposited a further 2 km inland of these
ridges. Finally, ridges 15 m high were sculptured into hull-
shaped forms with bedrock plucked from the flanks and
crest by helical flow that encompassed the whole height of
the ridge (Fig.
4.15
). A cockscomb-like protuberance sim-
ilar to that shown on the inverted keel-like stack in Fig.
3.24
was eroded towards the front of the ridge by intense vortices
or hydraulic hammering.
