Abstract:

Marine glacial landforms on the N-Iceland insular shelf demonstrate that offshore ice streams during the Last Glacial Maximum extended further to the north than previously inferred. The insular shelf is draped by ice-marginal and subglacial sedimentary features, megascale glacial lineations (MSGLs), moraines, eskers, and V-shaped, till ridge features, which have not been previously described in literature, possibly representing a push moraine or lateral crevasse-squeeze ridges. The offshore glacial landforms reflect the past ice flow directions of at least four major ice streams, from Skagafjörður into Skagafjarðardjúp, from Eyjafjörður into the southern Eyjafjarðaráll basin, from Bárðardalur into Skjálfandi and Skjálfandadjúp Basins, and from the Northern Volcanic Zone into the Öxarfjörður Basin. Megaflutes are orientated parallel to the direction of the major basins and the Kolbeinsey Ridge indicating that the ice streams were topographically constrained. The highly reflective V-shaped ridges within the more sediment starved Eyjafjarðaráll Basin are characterized by elongated “V-shape” formations with an average width of 300-500 m and an average length ranging from 400-1500 m, at a depth of 320-450 meters b.s.l. opening towards the flow direction of the main ice stream. The ridges change direction gradually, along with the basin curvature, from NNW-SSE in the southern part of the basin rotating to NNE-SSW, parallel to a 10 km long lateral moraine, which most likely separated two main ice streams. These ridges have not been identified elsewhere. Asymmetrical broad ridges interpreted as grounding zone wedges, up to 100 km offshore,  suggest that the deglaciation was episodic, with periods of standstill. Large normal faults within the Eyjafjarðaráll and Skjálfandadjúp Basins cut through the glacial features, reflecting tectonic activity throughout Holocene, also represented by current seismicity. Further mapping of the insular shelf is needed to refine models of ice streams from the Iceland Ice Sheet.

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