Trail 1: Mavis Grind - in the heart of the volcano
Granite / dolerite mixing
© Allen Fraser
The area of Mavis Grind is thought to
have once been a magma chamber,
feeding volcanoes such as the one
at Eshaness.
As you travel around here, see how
the road and cliffs cut through a
speckled grey rock. This is called
dolerite. About 370 million years
ago, this was a molten mass of rock
deep in the Earth’s crust.
Look closely - you will see thick red
coloured veins running through the
grey rock. This is a type of granite
magma that was injected into the
dolerite under immense pressure.
Look at the swirling patterns of red
and grey - these show how the
molten rocks partly mixed before
they solidified.
Crater / main vent
(now eroded away)
Volcanic plug
(Muckle Ossa)
Parasitic cone / side vent
(Kirn o Slettans)
Ronas Hill
© Davy Cooper
A magma chamber, filled with seething masses of molten rock is
the life source of a volcano. With enough time and pressure the
molten rock can fracture the rock around it, and reach the
surface as a volcanic eruption.
If you cross Mavis Grind and head
north you will see that the
landscape becomes steeper and
more rugged. This is a legacy of the
hard rocks - granite and gabbro which have been exposed by erosion
and moulded by glacier movement.
You cannot miss the great granite
‘whaleback’ of Ronas Hill Shetland’s highest point at 450m
(1486 feet).
Cone shape
Devonian
sandstone layers
Metamorphic rock
(former mountain chain)
Lava overlying
sandstone
(Braewick)
Magma chamber
(Mavis Grind / Ronas Hill)
Ramna
Stacks
Directions
By car / bike: Mavis Grind is on the A970, 35km (23 miles) north of
Lerwick.
On foot: 2km (1.25 miles) west of Brae.
Buses to Brae operate from Lerwick Bus Station.
Interpretation
ound
Yell S
• Geology wall
• Information Panel
Muckle
Ossa
Access
Ronas Hill
s
na
Ro
e
Vo
Facilities
Available in Brae.
Northmavine
Eshaness
Lighthouse
B9078
Braewick
Tangwick
Stennes
Brae
Muckle Roe
A970
Lerwick
© Allen Fraser
Mavis Grind
e
Vo
De
lti
ng
m
llo
Su
St Magnus Bay
Granite blockfield, Ronas Hill