Lava karst on W coast of Mull?

[Peter Ryder]

Last week had the pleasure of a paddle steamer cruise around the W coast of Mull, and on the W coast of Gometra (I think, could have been Ulva) spotted a whole series of big springs, close together, just above sea level. The geology here seems to be all Tertiary lavas. Could some form of lava karst be present? I have seen big springs from lava in Iceland. Anyone been to these parts? I don't think Mull has any limestone but stand to be corrected..

 

[Lankyman]

You must have been on the Waverley - we had the cruise to Crinan and the Gulf of Corrievreckan this Sunday gone.

On Mull I've been to MacKinnon's Cave and there are definitely speleothems in there that suggest carbonaceous rocks somewhere about

Formations in Mackinnon's Cave © Karl and Ali

Although the rocks that surround the sea cave aren't limestone it seems as though there are carbonate-bearing rocks around since there are places where various forms of small speleothems (calcite formations) are evident.

www.geograph.org.uk

'Cave coral' in Mackinnon's Cave © Karl and Ali cc-by-sa/2.0

Although the rocks that surround the cave aren't limestone it seems as though there are carbonate-bearing rocks around since there are places where various forms of small speleothems (calcite formations) are evident. I have seen identical formations to this in countless limestone caves in...

www.geograph.org.uk

Those streaks in your photo look very green. I wonder if they are some kind of seaweed kept going by sea water draining out of the lava?

 

[mikem]

There are thin beds, although don't know if this is same location (freshwater algae are also bright green):

The limestones of Scotland

webapps.bgs.ac.uk

 

[ChrisB]

I've found ammonite fossils at Carsaig Bay on the SE coast of Mull but I think that's shale. Wikipedia does mention a bit of limestone near Loch Don.

Gometra doesn't have cliffs of any size, maybe you were looking at the SW corner of Ulva? The big cliffs on the main island between Inchkenneth and Loch Scridain have lots of caves (and a fossil tree) shown on the OS map but I think they might be sandstone.

 

[Peter Ryder]

I've found ammonite fossils at Carsaig Bay on the SE coast of Mull but I think that's shale. Wikipedia does mention a bit of limestone near Loch Don.

Gometra doesn't have cliffs of any size, maybe you were looking at the SW corner of Ulva? The big cliffs on the main island between Inchkenneth and Loch Scridain have lots of caves (and a fossil tree) shown on the OS map but I think they might be sandstone.

Could well be Ulva, we did not have a map.

 

[Peter Ryder]

You must have been on the Waverley - we had the cruise to Crinan and the Gulf of Corrievreckan this Sunday gone.
View attachment 26324
On Mull I've been to MacKinnon's Cave and there are definitely speleothems in there that suggest carbonaceous rocks somewhere about

Formations in Mackinnon's Cave © Karl and Ali

Although the rocks that surround the sea cave aren't limestone it seems as though there are carbonate-bearing rocks around since there are places where various forms of small speleothems (calcite formations) are evident.

www.geograph.org.uk

'Cave coral' in Mackinnon's Cave © Karl and Ali cc-by-sa/2.0

Although the rocks that surround the cave aren't limestone it seems as though there are carbonate-bearing rocks around since there are places where various forms of small speleothems (calcite formations) are evident. I have seen identical formations to this in countless limestone caves in...

www.geograph.org.uk

Those streaks in your photo look very green. I wonder if they are some kind of seaweed kept going by sea water draining out of t

Some of springs seemed a bit above high tide level.. but not sure

 

[Andy Farrant]

You often get large springs in basaltic lava areas, as the base of lava flows are often composed of very rubbly broken up rock which are very permeable, particularly if the lava is of the A'a type, which is characterized by a rough, jagged generally clinkery fragments, as opposed to the pahoehoe lava. Plenty of places in Iceland where the drainage is underground. Some of the largest springs in the United States, discharging 5,000 cubic feet a second occur on the north side of the Snake River in Idaho, emanating from the base of a large flood basalt deposit. So you don't need limestone for large springs.

 

[mikem]

Gometra has one cliff listed on south side, Ulva has a couple (but no pictures):

https://www.ukclimbing.com/logbook/crags/gometra-13295/#photos&gid=1&pid=9

 

[mikem]

Various photos of the cliffs around the fossil tree on Mull itself (south of Ulva):

The Burg and Fossil Tree - Seaview bed and breakfast

Kilfinichen Bay near to the start of the Burg walk a sea eagle and otter hot spot!

iona-bed-breakfast-mull.com

 

[mrodoc]

Certainly some impressive basalt features round there.

 

[Peter Ryder]

Certainly some impressive basalt features round there.

Impressive