A 300-year surge history of the Drangajökull ice cap, northwest Iceland, and its maximum during the ‘Little Ice Age’

Abstract

Over the last 300 years, each of the three surge-type outlet glaciers of the Drangajökull ice cap in northwest Iceland has surged 2-4 times. There is valuable historical information available on the surge frequencies since the 'Little Ice Age' (LIA) maximum because of the proximity of the surging outlets, Reykjarfjarðarjökull, Leirufjarðarjökull and Kaldalónsjökull, to farms and pastures and monitoring of these glaciers since 1931. We have reconstructed the surge history of the Drangajökull ice cap, based on geomorphological mapping, sedimentological studies and review of historical records. Geomorphological mapping of the glacier forefields reveals twice as many end moraines as previously recognized. This indicates a higher surge interval than earlier perceived. A clear relationship between the surge interval and climate cannot be established. Surges were observed more frequently during the 19th century and the earliest 20th century compared with the relatively cool 18th century and the late 20th century, possibly reflecting a lack of information rather than a long quiescent phase of the glaciers. We have estimated the magnitude of the maximum surge events during the LIA by reconstruction of Digital Elevation Models (DEMs) that can be compared with modern DEMs. As reference points for the digital elevation modelling, we used the recently mapped lateral moraines and historical information on the exposure timing of nunataks. During the LIA maximum surge events, the outlet glaciers extended 3-4 km further down-valley than at present. Their ice volumes were at least 2-2.5 km 3 greater than in the beginning of the 21st century.

Architecture and structural evolution of an early Little Ice Age terminal moraine at the surge‐type glacier Múlajökull, Iceland

“…In morphological and architectural aspects, the Múlar moraine resembles terminal moraines of other glaciers in Iceland that surged beyond their previous maximum extent during the Little Ice Age into areas of a coherent sequence of loess, peat, and tephra [ Benediktsson et al ., , , ; Benediktsson , , ; Brynjólfsson et al ., , ]. We have little indications in our data of the hydrological conditions in the submarginal environment prior to and during the formation of the Múlar moraine.…”

“…A similar style and scope of moraine formation at temperate, surge‐type glaciers, with ductile deformation followed by brittle deformation, has been described from Brúarjökull and Eyjabakkajökull in eastern Iceland [ Croot , ; Benediktsson et al ., , , ; Benediktsson , ] and from Leirufjarðarjökull in northwest Iceland [ Brynjólfsson et al ., ]. Also, surges of the Bering Glacier in Alaska have been observed to override forested land causing ductile and brittle deformation of trees [ Fleisher et al ., ].…”

The origin of glacial alpine landscape in Tröllaskagi Peninsula (North Iceland)

“…In fact, these authors consider that this must be a usual process in the small Tröllaskagi glaciers. Surges, with no direct relationship to the climatic crises, were also very important in Vestfirðir (Brynjólfsson et al, 2014(Brynjólfsson et al, , 2015b. In any case, lichenometric studies of many glacial deposits in the Tröllaskagi cirques demonstrate that in the great majority of the cirques the main advance after Saksunarvatn tephra (10.2 ka) was during the LIA (Caseldine, 1987;Kugelmann, 1991;Häberle, 1991Häberle, , 1994.…”

Holocene tephrostratigraphy in Vestfirðir, NW Iceland

“…(f) Correlation of SKO 9.8, NEY 11.9, DAG 40 and REY 55.5 tephra layers to Sn‐1 (e.g. Larsen et al ., ; Brynjólfsson et al ., ). (g) Comparison of DAG 52, NHV 39.5 and NEY 17.9 to Katla E, and DAG 89 to Katla N (Hardardóttir et al ., 2001).…”

“…The silicic tephra layers from Leirufj€ orður were not geochemically analysed but were suggested to originate from the Hekla volcano. Additional tephra layers described from Vestfirðir are: the Hekla 1693 (Brynj olfsson et al, 2015;Harning et al, 2016a); V877/Settlement layer (Harning et al, 2018) and Sn-1 tephra from the Snaefellsj€ okull volcano (Harning et al, 2016b;Schomacker et al, 2016); Hekla 3 and Hekla 4, Brattihjalli tephra (Schomacker et al, 2016), Hekla T tephra and AIB-1/Hekla VF tephra all from the Hekla volcano (Harning et al, 2016b(Harning et al, , 2018. Recently, the Holocene tephrostratigraphy has been improved in the region, with several tephra layers reported from four lake sediment cores in Vestfirðir (Harning et al, 2018).…”