Ole Humlum

Origin of rock glaciers: Observations from Mellemfjord, Disko Island, Central West Greenland

Surface and interior characteristics of a tongue-shaped rock glacier at Mellemfjord on Disko Island are described. A long natural section shows the existence of a solid ice core. The implications for the origin of ice within the rock glacier and its surface debris layer are discussed and, from this, the rock glacier age is estimated at about 550 years; that is, it was probably initiated during the initial period of the Little Ice Age. It is suggested that the climatic control on ice-cored rock glaciers in particular is more pronounced than traditionally assumed. It is suggested that although the geomorphological feature described displays many characteristics of a normal glacier, it should be classified as a true rock glacier.

Rock Glacier Appearance Level and Rock Glacier Initiation Line Altitude: A Methodological Approach to the Study of Rock Glaciers

Two new concepts relating to rock glaciers are defined: the rock glacier appearance level (RAL) and the rock glacier initiation line altitude (RILA). The RAL may be regarded as an analogy to the glaciological concept glaciation level (GL) and indicates a critical summit altitude below which no rock glaciers occur. The RILA is a measure of the rock glacier head altitude and is situated below or at the local equilibrium line altitude (ELA) of glaciers.RAL and RILA have been mapped in a 370-km2 peninsula on the western coast of Disko, central West Greenland (70°N), where rock glaciers are numerous. Experience from this mapping indicates that when RAL and RILA values are compared with GL and ELA values, respectively, (1) different rock glacier generations may be differentiated and (2) rock glaciers belonging to the same generation may be differentiated as to being glacial or periglacial features. From this, some inferences as to their probable genesis may be drawn. The accumulation of snow appears to exercise...

Late-Holocene climate in central West Greenland: meteorological data and rock-glacier isotope evidence

The central West Greenland climate during the instrumental period since ad 1873 is analysed con cerning interannual and seasonal variations. A marked temperature rise was experienced from ad 1920 to 1930, especially affecting the winter season, after which the mean annual air temperature for ten years was about 3–5°C higher than during the previous period, effectively changing coastal central West Greenland from having the climatological character of a continuous permafrost region to a discontinuous permafrost region. Since then temperatures have gradually decreased, and are now approaching the Little Ice Age level experienced in the late nineteenth century and early twentieth century. Interannual twentieth-century temperature variations since ad 1923 have been substantial (5–15°C) for the winter season, intermediate (2–7°C) for the spring season, and smaller (1–2°C) regarding summer and autumn seasons. During the instrumental period the overall atmospheric circulation, rather than air temperature, appears to be the primary control on precipitation. A unique personal meteorological record for ad 1807–1808 is presented, outlining an early nineteenth-century central West Greenland climate which appears to have been rather warm, variable, stormy and wet compared to the late twentieth century climate. Analyses of the oxygen isotopic composition of ice samples from a ‘Little Ice Age’ glacier-derived rock glacier in Disko Island indicate a mean annual air temperature 2–4°C below present values, during cold intervals of the ‘Little Ice Age’. The potential of rock-glacier ice oxygen isotope data as a means of obtaining information on past climatic change within cold-climate high-relief areas is discussed. The ‘Little Ice Age’ in central West Greenland was presumably characterized by variable climate punctuated by intervals with severe cold winters, short summers, and glacier expansion during the last several centuries. Palaeoclimatic data like these from coastal Greenland represent supplementary information to ice-core data from the central part of the Greenland Ice Sheet.

Glacial History and Periglacial Landforms of the Zackenberg area, Northeast Greenland: Preliminary results

Christiansen, Hanne Hvidtfeldt & Ole Humlum: Glacial History and Periglacial Landforms of the Zackenberg area, Northeast Greenland: Preliminary results. Geografisk Tidsskrift 93:19–29. Copenhagen 1993. The geomorphology of the Zackenberg area has been investigated with the purpose of establishing a geomorphological map of a 260 km2 area around the planned research station. Production of a large digital three-dimensional elevation model, based on the use of a multi-model photogrammetric method, has been the basis for a GIS database and a topographical map (1:50,000) covering the investigation area. Both glacial and periglacial landforms have been mapped and a preliminary Late Weichselian glacial history of the Zackenberg area reconstructed. A monitoring of 11 selected test field sites representing climatically sensitive land elements has been established, enabling the registration of even minor short-term variations in the geomorphic processes.

Glacier behaviour and the influence of upper-air conditions during the Little Ice Age in Disko, central West Greenland.

Humlum, Ole: Glacier behaviour and the influence of upper-air conditions during the Little Ice Age in Disko, central West Greenland. Geografisk Tidsskrift 87: 1–12. Copenhagen, June 1987. An inventory of 205 glaciers and small firn areas in southwestern Disko, central West Greenland, display large differences as to the amount of ice recession since the end of the Little Ice Age. Especially high-situated ice bodies facing N and NW have experienced a substantial retreat, while other ice bodies have not. The cause for this difference is investigated by considering the amount of vertical equilibrium line displacement since the end of the Littel Ice Age. From this, it is argued that especially variations in upper-air wind conditions -as measured at the 850 mb level- are responsible for the observed heterogeneous glacial behaviour.

Altitudinal trends of talus-derived lobate rock glaciers on Disko, central West Greenland

Humlum. Ole: Altitudinal trends of talus-derived lobate rock glaciers on Disko, central West Greenland. Geografisk Tidsskrift 84: 35–39, Copenhagen. January 1984. Talus-derived lobate (TDL) rock glaciers follow the altitudinal trend of the equilibrium line (ELA) on contemporary glaciers, and based on an analysis of a cross-section, North Disko, it is suggested that the vertical distance between the zone of TDL-rock glaciers and the lowermost occurrence of tongue-shaped rock glaciers relate to the amount of precipitation.

Moraine Systems in the Faroe Islands: Glaciological and Climatological Implications

Abstract Danish Journal of Geography 96: 21–31, 1996. Geomorphological investigations on the Faroe Islands have shown the existence of small, but distinct moraine systems, indicating the former occurrence of glaciers. At least two glacial events may be distinguished: an older characterised by valley glaciers 2–4 km long, and a younger characterised by small cirque glaciers. Dating (14C) indicates that the youngest moraines are older than 5,200 yr. BP. During the two glacial events the largest glaciers were located in cirques facing NE, while the smallest were located in cirques facing SW. During the two glacial events equilibrium line altitude was at 200–350 m a.s.l. and 300–450 m a.s.l., respectively. Glaciers of intermediate size were found in cirques facing NW and SE. This pattern is interpreted as being caused by strong snow drift from SW and W. The temperature and precipitation values during the glacial events are discussed with reference to measured meteorological conditions at modern glaciers.

Natural cairns on rock glaciers as an indication of a solid ice core

Humlum, Ole: Natural cairns on rock glaciers as an indication of a solid ice core. Geografisk Tidsskrift 88:78–82. Copenhagen. 1988. A special surface feature taking the form of natural cairns is observed on rock glaciers in Disko, central West Greenland, known to possess a core of solid ice. These block accumulations are perceived as developed by the gradually outcropping of large en-glacial blocks from the ice core due to surface ablation, thereby lifting surface debris lying above. Below a line on the rock glacier where the surface debris layer equals or exceeds the depth of summer thaw, no more cairns are developed. Natural cairns as these on rock glaciers are suggested as a criterion for the existence of a solid ice core within the rock glacier, and the designation rock glacier cairn is proposed for them.

A Compilation of Radiocarbon Dates from Disko Bugt, Central West Greenland/Meteorological Observations in 1996 at the Arctic Station, Qeqertarsuaq (Godhavn), Central West Greenland/A Discussion on Pingos in Mellemfjord, Disko, Central West Greenland/Open System Pingos in Mellemfjord, Disko, Central West Greenland: A Reply to Gurney and Worsley

188 new and previously published radiocarbon dates on Holocene material from Disko Bugt, central West Greenland, are presented together with relevant informations (laboratory number, place name, dated material, geografic coordinates, altitude and δ13C-value) about the dates. In October 1990 an automatic weather station was established at the Arctic station (65 °15′N,53 °31′W), Qeqertarsuaq (Godhavn), Central West Greenland. The Station register parameters each 20 min., and the parameters have been described in an earlier paper in this journal by Nielsen et al. (1995). The present paper summarises main points of the climate during 1996. Open system, or more correctly, hydraulic pingos, are genetically poorly understood. A continuing problem concerns their need for a perennial groundwater supply (intra- or sub-permafrost). This has to be maintained despite the existence of continuous permafrost in many areas where they are located. Recent work on Disko Island has suggested a new type of hydraulic pingo deve...

High Deglaciation Rates in Denmark During the Late Weichselian - Implications for the Palaeoenvironment

Ole Humlum & Michael Houmark-Nielsen: High Deglaciation Rates in Denmark During the Late Weichselian—Implications for the Palaeoenvironment. Geografisk Tidsskrift, Danish Journal of Geography 94:xx-xx. Copenhagen, Dec. 1994. Available geologic evidence suggests that the mean deglaciation rate in Denmark 18,000–17,000 calendar years BP was at least about 100 m/year, probably requiring a total vertical ice ablation of 30–35 m/year. This ablation value is large when compared to the amount of ice ablation that could be expected on physical grounds. The reasons for this apparent discrepancy are discussed and factors such as glacier bed strength characteristics, presence of marginal water bodies and occurrence of strong catabatic winds are suggested as environmental phenomena that should be taken into consideration when formulating dynamic deglaciation models and reconstructing the Late Weichselian palaeoenvironment in Denmark; climate alone does not explain the observed patterns and rates of deglaciation.