Supplementary Material

Ice-shelf morphology
Further details of the morphology of the ice shelf are illustrated in Figure S1.

Ice facies
Six ice facies were identified in the ice-shelf margin, adjacent to Alexander Island, based on crystal size, bubble content and disseminated debris. These facies represent constituent components of foliation S2 and other surface features.
(i)	Coarse bubble-rich ice with a pale greenish blue hue and abundant air bubbles (Fig. S2A). Crystal size is approximately 1-3 cm. 
(ii)	Coarse bubble-poor ice with a greyish blue hue and evenly disseminated, well-spaced air bubbles. Crystal size is similar and this ice facies is gradational with the above facies. 
(iii)	Coarse clear ice with a dark blue or bluish grey hue with bubbles only at the crystal boundaries (Fig. S2A). Crystal size is approximately 2-4 cm.
(iv)	Coarse clear ice with up to 10% debris, typically disseminated mud and sand, with dispersed gravel clasts of multiple lithology and variable shape/roundness. Crystal size is approximately 2-4 cm. 
(v)	Fine-grained ice (Fig. S2B) with crystals typically a few millimetres in diameter.
(vi)	Candle ice (vertical ice crystals typically up to 0.5 m long and 2-3 cm in cross-section) associated with ponds (Fig. S2C).
Ice types (i) to (iv) are constituents of similar and isoclinal folds (Figs. S2D and E respectively). Fractures are defined by bubble planes (Fig. S2F). Typical ice-layer thickness measured in logs across vertical foliation orthogonal to the ice margin are illustrated in Figure S3.

Sediment facies analysis
This section describes and interprets the principal sedimentary facies that make up the ice-shelf moraine. Representative data are presented in Figure 9 of the paper; the full data-set is given in Figure S4.
Clast-rich sandy diamicton and muddy sandy gravel 
Description. Clast-rich sandy diamicton is derived from near-vertical debris-bearing foliation. On sublimating or melting out a massive diamicton is produced, consisting of up to 50% gravel clasts in a predominantly sandy matrix, but with some silt and minor clay. Clast roundness follows a broad range from very angular to rounded, with either angular/subangular or subangular/subrounded being the most abundant. Striations have been recorded on between 6 and 20% of clasts, and facets on 8 to 16%. The RA index is around 40. Clasts up to boulder-size are common, and there are some anomalous clusters of angular granite lying on the surface of the diamicton. Lithologies vary considerably along the coast; those identified include sedimentary and volcanic clasts of local origin and exotic intrusive and metamorphic clasts, probably from Palmer land.
The sandy gravel with minor mud lithofacies (>50% gravel) is also derived from near-vertical foliation. Although the proportion of gravel clasts is greater than for the diamicton, the fine fraction is similar, with sand dominant and a minor proportion of silt and minimal clay). Sandy gravel is mostly massive, although minor sorting has given a weakly stratified appearance in one section. Clasts show a range of roundness attributes from very angular to rounded, with angular and subangular dominant. Between 2 and 12% of clasts are striated, and 4-12% facetted. Clast lithologies show a similar range as for diamicton, and between 0 and 30% are Palmer Land igneous and metamorphic rocks.

Interpretation. Both clast-rich sandy diamicton and sandy gravel are the product of similar processes. There is clearly a mix of local (the majority) and far-travelled Palmer Land clasts. The roundness values and surface features of clasts, and their poor sorting indicate that debris has at some stage been carried in the zone of traction of a sliding ice mass. Palmer Land debris was initially entrained in Bertram Glacier before it flowed into the ice shelf. Either the ice shelf experienced basal freezing (Sugden & Clapperton, 1981) to trap the sediment as it crossed George VI Sound, or a thick fully grounded ice stream crossed the Sound. The latter scenario is deemed unlikely as the ice shelf disappeared in mid-Holocene time (Smith et al. 2007), and subsequent conditions are unlikely to have allowed a fully thick ice stream to develop. Furthermore, the bathymetry of the Sound, with a central ridge is not conducive to grounded ice flow across the Sound. As the ice mass impinged on Alexander Island it became grounded and local debris was incorporated. The proportion of local debris varies according to the already shattered state of the bedrock being eroded. Where high proportions of very angular and angular clasts from the Fossil Bluff Formation are present, it is suggested that clasts were little modified because of the short distance of transport. Clusters of angular granite boulders from Palmer Land may represent supraglacial transport, although the limited distribution of nunataks and derived flow paths do not support this.  The presence of rounded clasts is attributed to disaggregation of a conglomerate in the Fossil Bluff Formation, as this process was observed in a glacier in Ablation Valley below conglomerate cliffs.
	Once released from the foliated ice, especially where the ridges are steep-sided, during periods of melting the debris is prone to remobilization as debris flows, but this process little modifies the texture, except for winnowing out of small patches of fines.

Sandy gravel 
Description. Moderately well sorted pebble gravel with coarse sand matrix and occasional cobbles is associated with meltwater channels flowing over the above poorly sorted sediment, and with some debris flows. Clasts resemble those in the diamicton lithofacies in terms of shape and lithology.
Interpretation. This minor lithofacies is the product of debris flowage from which the fines have been winnowed out and clustering around flow lobes, or from more rigorous reworking by streams.

Sand
Description. Medium, well-sorted sand occurs on the otherwise clean ice-shelf surface in association with supraglacial streams and lakes. The sand shows braided characteristics and although it generally forms a thin veneer, pockets of sediment to a decimetre thick also occur, and there it is well stratified. Minor sand also occurs in small depressions in diamicton and sandy gravel.
Interpretation. The origin of sand on the clean ice shelf is not englacial, but is most likely to be aeolian, derived from the cliffs and loose material on eastern Alexander Island. The sand enhances ablation, encouraging supraglacial streams to develop. These rework the sand, and it collects in pools, which may then be abandoned. Sand pockets in areas of diamicton or sandy gravel are the winnowed products of debris flows.

References
Smith, J. A., Bentley, M. J., Hodgson, D. A., Roberts, S. J., Leng, M. J., Lloyd, J. M., Barrett, M. S., Bryant, C. L. & Sugden, D. E. 2007b. Oceanic and atmospheric forcing of early Holocene ice shelf retreat, George VI Ice Shelf, Antarctic Peninsula. Quaternary Science Reviews, 26, 500-516.
Sugden, D. E. & Clapperton, C. M. 1981. An ice-shelf moraine, George VI Sound, Antarctica. Annals of Glaciology, 2, 135-141.

Supplementary figures and table
Figure S1. Ice-shelf morphology. (A) General view of ice shelf and ice-shelf moraine looking towards Palmer Land; (B) ice cliff with thin debris layers adjacent to Moutonnée Lake; (C) aerial view of Ablation Lake ice tongue; (D) drained supraglacial lake with uneven sediment-draped floor and notches denoting former lake level; (E) pressure ridge of lake ice, Ablation Lake. 

Figure S2. Ice facies and structure at the margin of George VI Ice Shelf between Ablation Lake and Moutonnée Lake: (A) regular foliation S2, illustrating coarse bubbly ice (pale green) and coarse clear ice (dark blue) layers; (B) foliation S2 with anastomosing layers of fine-grained (light), coarse bubble-poor (darker blue) ice; (C) long crystals (c. 30 cm) of candle ice of lake origin upturned in a thrust lake-ice ridge, Ablation Lake; (D) similar fold (derived from S1 foliation) transposed within S2 foliation; (E) isoclinal fold of same structural context; (F) Closely spaced fractures defined by bubble planes. 

Figure S3. Representative logs through coast-parallel foliation S2 between Ablation Lake and Moutonnée Lake, illustrating the three main ice facies.

Figure S4. Complete data-set of sedimentological data: triangular plots of clast shape with ratios between a, b. c. axes; Clast roundness histograms; particle size distribution of sand-size and lower and pie chart of local clasts versus exotic clasts from Palmer Land.

Table S1. Characteristics of representative clasts in the ice-shelf moraine, based on thin-section analysis, with indication of their provenance. Sample locations indicated in Figure 4.