Kaldalon -- the big moraine and the Armuli raised marine terrace

 

The Jokulgardur terminal moraine, generally thought to be of Younger Dryas age, c 11,000 yrs BP.  It is by far the most prominent feature on the floor of the Kaldalon Valley. Marine sediments are exposed on its outer (western) edge.

In the latter part of this long article, Bout et al (1955) discuss the relationship between changing ice volumes and the raised marine terraces of Isafjardardjup.  But they do not seem to make a direct link between the big moraine in Kaldalon and the prominent marine tarrace north of Armuli, at the mouth of the Kaldalon trough.  That terrace, referred to as the 15 - 30m terrace by Bout et al, is the same terrace as that described by my colleagues and myself in 1975 as the 14 - 24m terrace. We need to be flexible in our labelling, because there are substantial variations in the altitude of the terrace top, and its edges are in places difficult to define.........

I am now rather convinced that this terrace represents a marine transgression or stillstand that coincided with the Younger Dryas ice expansion in Vestfirdir.  The is referred to as the "Younger Dryas glacial event" -- which may actually have been two events, incorporating the so-called Budi Moraine in south Iceland and other near-contemporaneous features.  Although global sea level was at c -60m at this time, there was also a contemporaneous very great isostatic load on NW Iceland, associated with a detached Vestfirdir ice cap which incorporated both Glamajokull and Drangajokull.  .  Isostatic uplift might have been slowed for maybe a thousand years, with the rate of uplift then approximately equivalent to the rate of eustatic sea-level rise.

Post-glacial (Holocene) sea-level curve, showing the stillstand or "step" near -60m around 11,000 - 12,000 years ago.  This was associated with the Younger Dryas "glacial event".

As David Sugden and I pointed out in 1962, there are marine sediments (including varved clays and bedded sands and silts) on the outer edge of the big terminal moraine called Jokulgardur or Holar.  These features have been missed or ignored by some other workers.  The sandur level adjacent to the western edge of the terminal moraine varies between 12m and 9m asl. The moraine top varies in altitude between 12m and 27m.  The surface is composed of unwashed till with a scatter of striated erratic boulders.  As far as we are aware, there are no marine terraces (with or without marine mollusca) on the inside of the moraine, even though the dry sandur level is at c 13m.  Therefore it is entirely logical to propose that at the time of the formation of the Armuli terrace glacier ice was blocking the valley as far west as the position of the moraine.  This in turn points to a grounded or floating ice edge.

https://www.researchgate.net/publication/262414815_The_Morphology_of_Kaldalon_a_Recently_Deglaciated_Valley_in_Iceland

The big terminal moraine in profile, seen from the southern gap.  Marine sediments are exposed in places on the steep west-facing slope.

Map of the moraine and features immediately up-valley.  From the DUVP 1974 Field Report.

Sketch map from Bout et al (1955) showing some features in Kaldalon and Skjaldfannardalur to the south.  In the latter valley there are abundant dead ice features linked to a delta near the valley entrance.  In 1976 we found traces of a high sea-level at c 30m on the SE flank of Steindorsfell.  We also estimated that at the time of rapid valley glacier ice wastage, relative sea level here was at 17.6m.  

Géomorphologie et Glaciologie en Islande centrale
 Pierre Bout, Jean Corbel, Max Derruau,  L. Garavel,  Charles-Pierre Péguy:
Norois  1955, vol  8,  pp. 461-574

https://www.persee.fr/doc/noroi_0029-182x_1955_num_8_1_1102

In Kaldalon the outermost moraine on the south shore is near the Kalda stream cutting, just to the west of the Seleyri spit (John and Sugden, 1962). Here there is a distinctive vegetation-free mound of till and striated boulders.  Moraine teraces extend for at least 500m along the valley side.  We speculated in 1962 that this might be a remnant of a terminal moraine, laid down on a grounded ice front at a time of relatively high sea level.  Could this be related to the 30m beach traces on Steindorsfell?

It's interesting that according to Hansom and Briggs (1991) the highest shoreline traces on Hornstrandir, 30 km to the north, are around 26m asl (Hjort et al, 1985).  We defined the upper marine limit as 30m in Skaldfannardalur -- and this is the same altitude recognised by Principato and Geirsdottir in 2002 and based on their own evidence.

Principato (2008) does not recognize the presence of the raised marine terrace at 24m - 14m  near Armuli, referring only to fragments of the very low terrace (which is referred to elsewhere as the "Nucella" terrace) and the marine limit near 30m.  I agree that neither of these can be "tied in" to the prominent moraines in Kaldalon.  But as mentioned above, I am convinced that the massive Jokulgardur moraine was formed at the same time as the 24-14m terrace.  A short-lived marine stillstand and a contemporaneous grounded ice front in Kaldalon -- that makes sense.  The delta moraine on the flank of Steindorsfell was formed at the same time, when the valleys of Skjaldfallardalur and Hraundalur were filled with ice.

My field map showing the main depositional features of the Armuli - Melgraseyri area.

The 24-14m terrace neat Melgraseyri, with the entrance to the Kaldalon trough beyond.  The "Nucella terrace" remnants are seen just above the present shoreline.