4c.2 purbeck rocks Flashcards
How geology matters
Geology has a significant impact on coastal
landscapes, and is arguably the most important factor
How geology matters
Rock structure (or big-scale geology) means the way
between areas only emerge as processes act on the rock to create
that different bands or types or rock are arranged in
different landforms.
relation to the coastline.
How geology matters
Some coastlines are concordant (rocks are arranged in
work: abrasion, attrition, hydraulic action and solution/corrosion.
parallel), others are discordant (rocks are arranged
•Small scale geology also matters. Sedimentary rocks like chalk are
perpendicular)
How geology matters
Discordant coastlines often result in bays and
•Where these are found and headlands, these weak points are often
headlands forming. The different types of rock erode
exposed leading to a sequence of events that form caves, arches,
at differing rates, mainly due to their relative
stacks and stumps.
resistance to erosion
How geology matters
coastlines are characterised by hard rock
•Marine (i.e. erosion from the sea) can also result in the formation of
headlands with cliffs and soft rock bays with beaches.
How geology matters
coastlines tend to reach equilibrium, with the
collapses, is eroded and leaves behind a platform at the low-water
sea’s erosive power increasingly concentrated on
mark.
exposed headlands (which are more resistant) and
lower energy waves being found in bays (due to wave
refraction)
how geology interacts with processes
•Rock types in themselves don’t change the coastline. The differences
Rock structure (or big-scale geology) means the way
between areas only emerge as processes act on the rock to create
that different bands or types or rock are arranged in
different landforms.
how geology interacts with processes
•Small scale geology also matters. Sedimentary rocks like
often characterised by weak points, called joints and bedding planes.
how geology interacts with processes
•Where these are found and headlands, these weak points are often
headlands forming. The different types of rock erode
exposed leading to a sequence of events that form caves, arches,
at differing rates, mainly due to their relative
stacks and stumps.
how geology interacts with processes
•Marine (i.e. erosion from the sea) can also result in the formation of
wave-cut platforms where notches are formed at the base of hard-
rock cliffs due to wave action (abrasion and hydraulic action). The cliff
collapses, is eroded and leaves behind a platform at the low-water mark
Abrasion
when rocks and other materials carried by the sea are picked up by strong waves and thrown against the coastline causing more material to be broken off and carried away by the sea.
Attrition
when rocks that the sea is carrying knock against each other.
Hydraulic action
the sheer force of water crashing against the coastline causing material to be dislodged and carried away by the sea.
Corrosion
the process of mechanical erosion of the earth’s surface caused when materials are transported across it by running water, waves, glaciers, wind or gravitational movement downslope.
