Isles of Scilly on the agenda

 Illustration from Hiemstra et al, 2006

Tomorrow I'm off for a short holiday on the Isles of Scilly with my wife and four old friends.  Should be fun, if it's not too cold and wet.......

I have mentioned the islands many times on this blog, but have never been there before -- and I hope I can escape from the madding crowds now and then in order to do a bit of geomorfin'........

There are some rather interesting questions still to be answered with respect to this archipelago.

1.  Was the glacier ice that reached the islands in the Late Devensian (the dating seems to be pretty secure) really in the form of a "surge lobe" which pushes southwards from the St George's Channell to the Scillies and beyond?  As I have said many times before, this defies some of the laws of glacier physics, and I have real problems in accepting that a lobe like this could have had the form shown in the top left diagram. There must have been a calving bay with a concave shape at its outer end, and it must have spread laterally rather than flowing as a narrow lobe.  (Ice only flows in the manner shown when it is constrained within a clearly defined channel.  Such a channel does not exist in the Celtic Sea, and there is no evidence that it ever did.)

2.  To what extent are the curving depositional features on the northern islands related to actual moraines that once marked ice edge positions?  The evidence presented in various papers looks pretty convincing....

3.  Does the limit of the Hell Bay Gravel actually delimit the maximum ice extent during the Devensian?  Ice limits are often more difficult to define than one might imagine!

This map is from the Isles of Scilly chapter by James Scourse, published in the GCR review for SW England (1998).  Many other authors have suggested similar limits, and it will be good to see some of the evidence on the ground.

4.  In most of the recent literature on the glaciation of the Isles of Scilly it is claimed that the Devensian Irish Sea Glacier had a greater extent (at least in the Celtic Sea arena) than any of the earlier glaciations of the current ice age.  Scourse claims this, as do others with whom he has worked -- and yet there appear to be "widespread" erratics in some exposures of the "Watermill Sands and Gravels" which  underlie and pre-date any of the Devensian periglacial and glacial deposits on the islands.  Was there an older and more extensive glaciation, or was there not?  It will be interesting to check out the evidence on the ground. (Watermill Cove, the type locality for these early deposits, is on the isle of St Mary's, where we are staying -- so I shall certainly check it out.  It's well to the south of the Devensian glacial limit as currently defined.)

5.  How many raised beaches are there?  Some writers say one, and others say two.......

6.  What are the similarities between the Isles of Scilly and Pembrokeshire?  The Devensian stratigraphy does appear, from the descriptions, to be closely correlated.