The Trimbilsstadir double moraine

The Kaldalon "valley side esker" (now interpreted as a moraine) seen from the north.  The steep ice contact face is prominent, facing up-valley.  The older, subdued moraine is seen to the right, in contact with the outer slope..  

Satellite image of the Trimbilsstadur moraine / kame complex.  the outer (older) ridge is subdued and well vegetated.  The inner, very prominent, ridge is not grassed over to the same extent, and has a steep up-valley face interpreted as an ice contact slope.  The associated linear kame terraces (or lateral moraines!) are seen right of centre.

This troublesome and confusing landform has been the subject of much debate in the literature, and I think that our 1962 designation of the large curved ridge (on the inside or eastern flank of the subdued green moraine)  as a "valley side esker" was somewhat naive and premature.  Others who have examined the feature more recently seem to be convinced that it is made primarily of till, not fluvioglacial sands and gravels, and that is important information.

David Sugden and I always were a bit worried about an apparent "esker" being formed this high on a valley slope -- especially since eskers always form in tunnels with ice above and on either side of them.  The eskers on the floor of the valley do seem to have been formed in sinuous tunnels beneath a wasting glacier, and they are linked into assorted hummocky dead-ice features and also to an abandoned outwash fan.  But here on the hillside it is difficult to conceive of "containing"  ice on the down-valley flank.  Neither do the conditions exist for classic kame terrace formation, in contrast to other situations further up the valley........

So I now revise my opinion, and think that this feature is a remnant of a terminal moraine with a very sharply defined up-valley ice contact face.  The feature is also much fresher than the subdued well vegetated moraine on its outer edge -- so it has to be younger.

I think we can also say something about the nature of the glacier advance associated with the ridge.  Because there is a substantial "void" on the up-glacier flank, this suggests to me a very rapid and dramatic ice advance involving relatively clean ice.  (If the advance had been more gradual and prolonged, the ice would have been heavily laden with supraglacial and englacial debris, and this load, when dumped, would have left a dramatic expression in the landscape.)

So going with the theory that this moraine was formed around 1740, what do we know about this advance?  Now we would call it a surge.   The old records refer to a great readvance between 1700 and 1756, in which the glacier covered once green meadows and destroyed the farm of Trimbilsstadir.  The ice front moved forward by at least 2 km.  There are also records of a great "glacier burst" or jokulhlaup in Kaldalon in 1741.  This suggests massive quantities of meltwater associated with a catastrophic ice wastage event.

I think we have no option but to argue that there were TWO surge advances here, ending up in virtually the same place.  Coincidence?  Or was there cause and effect?   Of course, it is quite possible that the older moraine was once more extensive, and that it did act as something oif a barrier to the advance that occurred around 1740.

Ages?  From the evidence presented by other workers, it is most likely that the old green moraine is of Neoglacial age, maybe dating to 3500 - 2500 yrs BP, and that the newer moraine segment dates from the Little Ice Age surge that occurred around 1740.

The "matching feature" on the north side of the valley, which I have referred to as the Kegsir Moraine, is even more copmplex, with incorporated distorted peats and other layers demonstrating a bulldozing effect diuring one of both of the advance phases.