Rocks - Pillow Lava
When basaltic lava erupts under water it takes on a particular lumpy morphology which gives it it's name: pillow lava. The water supercools the outer layer of basalt to form an ultra fine grained chilled margin which acts as a skin to each pillow.
The stone "pillows" continue for a short period to behave behave as fluid bodies within their chilled carapace, and sag into the pillows below them solidifying completely.
allows for the way-up of pillow lava flows to be deduced
You can also examine a thin-section of the Arran pillow lava shown above.
|INDEXES REFERENCES ACKNOWLEDGEMENTS|