Why the regional marine limit (highest shoreline) is difficult to find

 

I came across this fabulous oblique aerial shot the other day, of part of the coast of Svalvbard.  I have labelled some of the features.

In the early days of our cvareers, David Sugden and I became quite good at finding the regional marine limit as we hoofed around in the landscape.  We discovered one marine limit at 134m in Kjove Land, East Greenland, in 1962, and then another one at the staggering  altitude of 275m at Noel Hill in the South Shetland Islands in Antarctica in 1966.  The altitudes were fixed with the most primitive surveying instruments coupled with barometric checks.  There were no detailed maps, and no GPS instruments in those far-off days.......

In the period since we did our fieldwork, as far as we know nobody has found higher marine traces in our fieldwork areas, or corrected our altitudes.

The marine limit in a glaciated landscape subject to isostatic adjustment or tectonic uplift is notoriously difficult to find.  The reason is explained in the photo above.  At the end of a glacial episode, as ice wastage speeds up and as isostatic uplift kicks in, very little of the coastline is initially subject to wave attack and other coastal processes.  That is becaused of the protection afforded to the coastline by a band of landfast perennial sea ice -- sometimes called the "ice foot".  It's very clear in the photo.  In the deepest valleys or fjords, flowing glaciers with floating snouts effectively protect coastal solid rock outcrops, and in other embayments seasonal sea ice may also afford protection.  We can see this situation at the left edge of the photo.

In the photo only one small coastal stretch is in contact with the open sea -- and this is where a range of coastal processes can operate -- just for a short time if isostatic or tectonic uplift rates are high.  So on the ground today we may find washed surfaces, small pebble banks or simply till deposits from which some of the finer sediments have been removed by wave action.  I recall many intense discussions with Dave while we tried to piece together the clues!  And because of the relatively great age of these high beach remnants, they have of course also been modified by post-glacial slope processes and frost shattering.

In the case of the South Shetland Islands, there was reasonable evidence of a short-lived ice advance over the marine shoreline traces.  It was clearly not very powerful, since the traces were well preserved.  Some have suggested that the "residual raised beach" that we described may be Plio-Pleistocene in age;  I disagree with that, since the remnants are so close to an ice edge that they cannot possibly have survived for that long, during multiple expansions and contractions of the  King George Island ice cap or indeed the regional ice sheet cover.  On the other hand, away from the areas of distinct ice streaming, island ice caps can expand to cover pereviously ice-free areas and can actually protect them.  So, on balance, in my 1971 paper I suggested that the Noel Hill resudual beach may well date from the last interglacial......... Eemian or Ipswichian.

Thus far, nobody, as far as I know, has managed to date these "high level" raised marine features which David and I described in our big paper in 1971........

See also:

https://brian-mountainman.blogspot.com/2025/02/the-noel-hill-residual-raised-beach.html