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13
UNSEEN CHANGES
THE CLIFFS of the coast of the North York Moors National Park
are predominantly formed of hard rocks from the Jurassic and
Cretaceous periods. They appear stable, with the exception
of abrasion caused by incoming tides and waves. But closer
inspection reveals that the cliffs are not only eroding at the toe,
but across the entire cliff face, although this is easy to miss when
observing them by eye alone.
Changes in coastal cliffs are difficult to spot because they are
sometimes so slow or subtle that they go undetected. Using aerial
photography for surveying cliffs is limited in practice, particularly
on steep rock faces that are obscured when viewed from above.
In order to understand these unseen changes taking place in the
coastal cliffs that can lead to collapse, new techniques are needed
that allow researchers to monitor coastal cliffs more accurately
and over long time periods. Fortunately, there is an advanced
technology available that helps geoscientists to monitor the
cliffs in ways never before possible. This technique is known as
Terrestrial Laser Scanning (TLS).
3D point cloud of cliffs at North York Moors National Park.
Terrestrial laser scanner.
A TERRESTRIAL LASER SCANNER is equivalent to a 3D
camera but instead of capturing a coloured pixel for every
position upon the cliff, as with a digital camera, it uses a laser
to measure the shape of the cliff to build a 3D point cloud
of the surface. Comparing this data month to month helps
researchers to monitor the underlying changes in rock cliffs
that are otherwise invisible to the eye.
‘It’s accurate’, says Rosser, ‘it’s fast and convenient because
you don’t have to go near the cliff, and we can capture
extensive sections of the coast within one survey. The system
captures data at very high-resolution, measuring the cliff
surface every 3–5 cm across the face’.
Rosser’s research team travel to the same part of the coastline
in the North York Moors National Park each month to capture
the shape of the cliffs. The laser scanning system is fast
enough to allow researchers to scan 3 km of the coastline in
only one visit. They have been doing this