Volcano of the Week!

20/01/2014-26/01/2014

Having been to Edinburgh to Volcano and Magmatic Studies Group (VMSG) annual conference, it would only be right to give this week’s title to Arthur’s Seat!

This week’s volcano of the week is:

Arthur’s Seat

Location: Holyrood Park, Edinburgh, UK

Type: Volcanic remnants

Elevation: 251 m, 823 ft

Last Eruption: Around 340 million years ago (Carboniferous period)

Status: Extinct

Details:

Although Arthur’s Seat was last active 340 million years ago, the remains of this extinct volcano holds great importance to modern geology. Arthur’s Seat was formed when what is now known as Scotland was by the equator surrounded by tropical seas. The volcano’s eruption followed on from Castle Volcano’s eruption; which is now the location of Edinburgh’s castle. At Arthur’s Seat, eruption of lava first took place at what is called the Lion’s Head, followed by eruptions at the Lion’s Haunch. The cone of the volcano took form after numerous eruptions of lava and ash.

After the volcano became extinct, it became buried under sediments. Following on from this, more molten magma intruded horizontally to form Sailsbury Crags. The structure of the volcano was tilted eastwards due to earth’s movements and the final stage involved millions of years of erosion by both weathering and glaciers during the Ice Age to expose the internal structure of the volcano. What remains today is less than half of the original structure and height of the volcano. You can see examples of numerous lava flows, pyroclast deposits, ash, agglomerates, sills and dykes at Arthur’s Seat.

In the 18^th century, James Hutton used Arthur’s Seat to support his theory on geological process such as the formation of igneous rocks over millions over years. He used the site at Sailsbury Crags which show magmatic intrusion. This site is now known as Hutton’s Section. Sailsbury Crags is an example of basalt intrusion which occurred millions of years ago after Arthusr’s Seat volcano became extinct. At Hutton’s Section, as shown on photos you can see an example of basalt forcefully intruding a layer of sandstone.

                                          A view of Arthur’s Seat Volcano

Hutton’s Section

                                         Hutton’s Section: A closer view of the basalt intrusion

                           Hutton’s Section: Basalt forcefully intruding sandstone pushing it upwards.

Hutton’s Rock: This is a vein containing Hematite. It was left unquarried at Hutton’s request and is therefore also an example of environmental conversation.

                                                                      Lava Flow 2

Pyroclast and ash deposits from the volcano