SEDIMENTOLOGICAL ANALYSIS OF A LATERAL MORAINE, GÍGJÖKULL, ICELAND

Frontal and lateral moraines are large prominent landforms found in glaciated valley environments and commonly dam large proglacial lakes. Due to recent rapid deglaciation, there is an increase in the size and number of these proglacial lakes, enhancing the possibility of glacial lake outburst floods (GLOFs), which can have devastating impacts on communities located down valley. Unfortunately, relatively little is known about the sedimentary architecture of such large moraines or their potential for failure due to the inaccessible nature of moraine faces. This study uses Unmanned Aerial Vehicle (UAV) derived photographic analysis to identify and characterize the sedimentary architecture of the eastern lateral moraine of Gígjökull in southern Iceland.

Seven lithofacies were identified within the moraine from UAV imagery including massive, clast-supported diamict (Dcm), crudely-stratified, clast supported diamict (Dcs), crudely-stratified, matrix-supported diamict (Dms), massive-matrix supported diamict (Dmm), gravel (Gm, Gms), and fine grained facies (Fl, Fd). These facies types were grouped into three lithofacies associations (LFAs) on the basis of their lateral and vertical facies relationships, bed contacts and the architecture of the sedimentary units. LFA 1 consists of stacked units of massive and matrix-supported diamict (Dmm, Dms) and is interpreted as originating from matrix-rich subaerial debris flows generated from englacial and supraglacial positions. In contrast, LFA 2 is much coarser grained, consisting predominantly of crudely stratified and clast-supported diamict (Dcm, Dcs) with angular to subangular clasts that originated primarily from rockfalls or avalanches. LFA 3 consists of deformed matrix-supported diamict (Dms, Dmm) that shows both brittle and ductile deformation and is interpreted as a fine-grained ice marginal deposit glaciotectonized during glacier expansion/overriding. Each of these lithofacies associations dip away from the current ice margin at between 10° and 25° and record changing sediment supply conditions during moraine formation. The UAV photogrammetric methodology used in this study allows analysis of inaccessible exposures and will facilitate enhanced understanding of the complex sedimentary architectures of large moraines elsewhere.