Glacier thermal regime linked to processes of annual moraine formation at Midtdalsbreen, southern Norway

Abstract

Glacier thermal regime is shown to have a significant influence on the formation of ice‐marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up‐glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast‐form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin (<10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge‐shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ∼40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the Little Ice Age and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze‐on, which requires stable glacier geometry. While the annual moraines on the eastern side of Midtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice‐stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold‐based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought.

Simulating the evolution of Hardangerjøkulen ice cap in southern Norway since the mid-Holocene and its sensitivity to climate change

“…2.1.2, Hardangerjøkulen can be characterized as a temperate ice cap. To the contrary, temperature measurements suggest that Midtdalsbreen has local cold-based areas at its terminus (Hagen, 1978;Konnestad, 1996;Reinardy et al, 2013). However, we expect that this has a minor effect on the large-scale ice flow of Midtdalsbreen and Hardangerjøkulen.…”

Topographic controls on plateau icefield recession: insights from the Younger Dryas Monadhliath Icefield, Scotland

“…The distances (10–60 m) between moraine crestlines are similar to distances on Skye (Benn, ) and in the Northwest Highlands (Lukas and Benn, ), and recently formed annual moraines in Europe (Lukas, ; Reinardy et al ., ; Chandler et al ., ). The number of ice margins (12–99) is significantly lower than recognized in the Northwest Highlands (53–210; Lukas and Benn, ), however.…”

Characteristics of recessional moraines at a temperate glacier in SE Iceland: Insights into patterns, rates and drivers of glacier retreat

“…Proglacial materials may also begin to build up and be pushed as the ice-front continues to re-781 advance (Reinardy et al, 2013). During the spring (3), this frozen-on sediment begins to melt 782 out incrementally, forming a ridge containing diamicton, gravel and sand units dipping 783…”