Mynydd Preseli - Pembrokeshire
Carn Alw - Rhyolite with Flow Banding
A boulder to the west of Carn Alw showing Flow Banding.
Due to the high silica content, Rhyolite Volcanic lava is very viscous and flows slowly.
Flow banding , which manifests as a banded, streaky appearance / swirling layers
of different color or granule size .
Caused by friction of the viscous magma in contact with a solid rock interface, usually
the wall rock to an intrusive chamber or if the magma is erupted, the surface of the
earth across which a lava is flowing.
Ref: 12122.3
Date: 01/08/2013
Location: SN 1371 3380
