Caves, blowholes, geos, stacks and arches: a classic
coastline of erosion at Eshaness, Shetland
The outer coast of Shetland is one of the best places in the world to study the erosion
of hard rock coasts.
1. Why is this?
A. Wave energy
B. Rock type
(http://www.fettes.com/shetland/Geology_Shetlland/I
mages/geology%20sketch%20map.jpg)
2. The Grind of the Navir
This headland at the north end of Eshaness is formed in flows of ignimbrite, a
resistant volcanic rock (Figure 1.). What is the dip and strike of the flow?
Figure 1. The Grind of the Navir viewed from the south.
3. Geos and caves
On Google Maps you can see that the cliffline is indented with many clefts or geos.
A. Calder’s or Calders Geo
Locate this and estimate the length of the geo.
B. Look at http://www.fettes.com/shetland/geo.htm
How do geos form? Refer to hydraulic action and rock fracturing.
C. The Holes of Scraada
Locate this. How long is this sea cave?
How long is the geo?
Suggest how this cave formed. What has happened to it subsequently?
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4. Blowholes or gloups
This diagram of The Grind of the Navir shows a blowhole. What is it? Photo A shows
that the headland is crossed by E-W and S-N trending fractures. Suggest how the
blowhole might have formed.
5. The Dore Holm: arches
A. Find and insert a good image of this island and its arch
B. How have rock type, rock structure, wave energy and wave refraction combined to
form this impressive feature?
6. The Drongs: stacks
A. Find and insert an image of these stacks
B. The rock type is granite. What names is given to the sets of vertical fractures that
determine the walls of the stacks?
C. Why have only stacks and no arches formed at The Drongs?
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