Scottish Devonian Volcanoes
There have been various times in Scotland’s
3 billion year history when the land has been dotted with active volcanoes
and the Devonian was
one of these times. In most places, the volcanoes themselves have long
since been eroded away, though in places, the remains of the lava flows
can be found forming large tracts of land today. Elsewhere, the land has been
eroded so much that the ancient magma
chambers (where the molten magma has long since cooled to form granite) from
deep beneath the volcanoes have been exposed at the surface today. These large
granite bodies
can be found for example at the Cairngorms, Glen Etive and Dalbeattie. As granite
is such a hard rock, these bodies often form hills.
But although Devonian volcanoes
were common, hot springs were rare. The hot springs were caused by
the surfacing of geothermal water – water that was heated
by being close to an active volcano. These geothermal waters were rich in dissolved
silica, the main chemical ingredient of the mineral quartz. When the waters came
to the surface and evaporated, the silica cooled and hardened to form a sinter.
Over time,
this sinter was altered to the chert that we find today.
