Ice front stillstands in the Kaldalon Outlet Trough

 

Top image: Annotated satellite image showing the main geomorphological features of the middle section of the Kaldalon valley.  Based on mapping and field notes from many visits in 1960 and 1973-77.  The literature is filled with references to multiple ice front stillstands, with each one now assumed to coincide with a glacier surge. 

Sketch map:  suggested ice front positions.  The 1780 position is  interpolated from historical records; The 1740 and 1820 positions are based on the mapping of terminal moraine remnants.

There is much accumulated evidence to show that the massive moraine which is the most prominent feature of the depositional landscape is of Younger Dryas age, around 12,000 years BP.  All of the ice front positions recorded on the up-valley side of that moraine must be younger.  It would be tempting to refer to thes as "recessional moraines", but that would be inadequate, since Kaldalonsjökull is one of a group of Drangajökull surging glaciers with a history of spectacular advances of up to 1 km.  Not all of these advances are recorded in the landscape, since now and then large advances might have wiped out the traces of prior (less extensive) retreats and advances........

According to Brynjolfsson et al, there are traces of seven surges, as shown on this image:

There is a certain amount of guesswork involved, because not all advances are recorded by strong linear features such as terminal and lateral moraines, and the valley floor is continuously reorganized -- and raised -- by the shifting sandur of the Morilla River.  There may be many buried moraine fragments related to the five morainic mounds which we referred to in 1960 as "the Green Mounds". 

The MOR 3 morainic ridge (assumed to date from c 1820) was described in detail in the article by David Sugden and myself in 1962, on p 359.  We described abundant fluvioglacial sands and gravels resting on top of morainic material with large striated boulders.  

There have also been catastrophic events:  Quote:  Moraines 4, 5 and 6, described below, are not recognizable  anymore, because of a 1998 outburst flood in the glacial river Mórilla, which drains Kaldalónsjökull (Sigur›sson, 2000). The river transported icebergs of many metres in diameter 2–3 km 

down-valley and deposited an 8- to 10-m thick sheet of coarsegrained gravel on the valley floor distal to the glacier margin. A thinner sheet of gravel was deposited to about 1 km down-valley.

Ice edge positions MOR 4, 5, 6, and 7 are based largely on literary sources, and are approximate only.

The 1740 surge moved the ice front down-valley by at least 1.5 km, and the 1994-1999 surge is known from detailed records to have moved the ice front downvalley by around 1 km.  In between these in the timeline, there were five known surges which involved advances of between 300m and 500m.  

My own map of possible surges and ice edge positions is below:

Were there Neoglacial advances?

There is considerable discussion in the literature about the events of the Neoglacial (the period from about 3,500 yrs BP to about 2,000 yrs BP, during the Holocene.  The labelling is not very satisfactory, since in many areas this period (following the Hypsithermal or Climatic Optimum period, 8,000 - 3,500 yrs BP) was marked by the persistence of relatively warm conditions.  During the Hypsithermal episode many smaller ice masses wasted away completely, whilst in other areas there was renewed glacial activity as a consequence of localised climatic shifts and increases in precipitation.

AI generated chart showing climate oscillations in the Atlantic arena

https://doi.org/10.1177/0959683615576232

Principato and others suggest that the Neoglacial advance of the Drangajökull glaciers was greater than any of the advances associated with Little Ice Age surges -- and the evidence from Leirufjördur and ~Reykjafjördur seems persuasive.  In the Kaldalon trough the evidence is more difficult to interpret, and hinges partly on the interpretation of contorted (ice pushed?) peat beds and other organic layers exposed on the flanks of the Kegsir and Trimbilsstadir moraines.

Stream cutting on the outer edge of the Kegsir Moraine, excavated and described by the members of the Durham University Vestfirdir Project, 1973-77.  Here there are distorted, ice-pushed organic sediment layers including peat beds.

 

We studied the Kegsir moraine in 1975 and 1976, and obtained the following radiocarbon dates from wood fragments contained within contorted peaty layers:

Section A -- depth 295 cm. Wood fragments in basal gravel and stones, 7115 +/- 125 yrs BP (St 5634)

Section A -- depth 260 cm.  Wood fragments in peaty and stony grey silt, 3535 +/- 125 yrs BP (St 5634)

Section C -- depth c 315 cm.  Wood fragments in grey stony gravel, 4170 +/- 95 yrs (St 6051)

Section B -- depth 35 cm.  Wood fragmnents in peat above stony gravelly layer, 255 +/- 95 yrs (St 6050)

These radiocarbon dating results should be interpreted alongside these as reported by Principato.  Samples taken from an apparently undisturbed peaty layer not far from our sampling site gave dates of 3328 +/- 45 yrs BP,  2503 +/- 59 yrs BP and  2623 m+/- 68 yrs BP from wood fragments and mossy materials beneath an ash layer which was itself covered by thin layers of sands and gravels.  Another sample from an unidentified  peat layer is dated at 1296 +/- 39 yrs BP  (Table 1 from Principato 2008).  Might the ash layer date from the Hekla 1104 eruption or one of the others known in the record?  A sample taken from the Trimbilsstadir moraine on the south side of the valley does suggest this association.

Principato (2008) claims that tephra layers found in the "green moraine" on the north side of Kaldalon point to a glacial readvance event in Kaldalon at around 2600-3000 yrs BP.  But her radiocarbion dates appear to contradict this, suggesting that this was a time of peat and tree / shrub growth............  There is a dating dilemma here, which will no doubt be resolved in future work.

Principato claims that there was at least one Neoglacial advance in Kaldalon which was more extensive than any of the Little Ice Age advances.  That may be true, but there are just a few metres in it.  The "double moraine" at Trimbilsstadir shows two readvances to almost the same position. 

At face value, the radiocarbon evidence from the Kegsir Moraine shows that there was tree or shrub growth in the valley from c 7000 yrs BP to c 3500 yrs BP --  and at some stage after that, there was an ice advance which disrupted the organic sediments and possibly resulted in the formation of a push moraine.  Other evidence suggests a date of around 3000 - 2600 yrs BP for this event in Kaldalon -- and that seems reasonable.  One event or several?  The jury is still out.

The Kegsir Moraine and the Trimbilsstadir moraine are both complex features which have attracted much discussion.  I think it is quite possible that the Kaldalon glacier has advanced to this position on two -- or possibly three -- separate occasions, first in the Neoglacial and then again in the Little Ice Age, in 1740 and possibly 1780.

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The outermost Kaldalon terminal moraine

The big Younger Dryas moraine (Jokulgardur) is not the oldest or outermost moraine in the glacial trough.  There are remnants of a much earlier moraine on the south shore near the trough exit, just to the west of the Seleyri spit.  There is a substantial mound of moraine above the road, and till is exposed in the cutting of the Kolda stream.  This is over 4 km beyond the Jokulgardur moraine.

Exposure of the outermost moraine in the Kaldalon trough.  The Seleyri spit can be seen in the distance.

Nothing is known about thye age of the moraine, but it must be Late Glacial, formed either during a readvance prior to the Allerod Interstadial, or else a retreat stage during the earlier deglaciation of the Vestfirdir Peninsula, at a time of higher sea level.

The boulders that litter the tidal mud flats in Kaldalon -- or at least some of them -- might be ralated to this outermost glacial stillstand stage.....