Introduction to glaciated valley landsystems

Glaciated valley landsystems refer to the landforms and sediments produced by valley glaciers in upland and mountainous environments¹. As valley glaciers currently exist under a broad range of topographic and climatic settings across the globe^2,3, the landsystems they create are equally varied.

The glaciated valley landsystems section of ‘AntarcticGlaciers’ will give examples of the range of different landscapes formed by valley glaciers. But before diving into specific examples, we suggest reading this page, which outlines the broad controls on the ‘style’ of valley glacier and the landforms and sediments they create.

Valley glaciers exist in many mountain ranges across the globe. The valley glacier pictured above, the Alestchgletscher, flows from the Jungfrau mountain area in the Swiss Alps. Photo: D. Beyer

What valley glaciers have in common

Let’s first look at what nearly all valley glaciers have in common. Most important, valley glacier behaviour and the landforms they create is largely related to two main factors¹:

Topography, which strongly controls glacier size and shape (known as its morphology), as well as the transfer of mass (ice) and debris. As all valley glaciers are, by definition, confined by valley walls, their flow and interaction with the land surface is closely related to topography.
The amount of rock and sediment debris received from adjacent valley sides and carried at the ice surface (which, as we’ll see below, varies from glacier–to–glacier).

Fox Glacier in New Zealand (2013). Note that debris from the valley side has partly covered the ice surface. Photo: M. Basler

What controls valley glacier style?

Topography

Topography is important at several scales.

At the largest scale, the tectonic history of a region defines the size, number and altitude of mountains where glaciers can exist³. Valley glaciers occupying the highest mountain ranges, such as the Himalayas, for example, exist under a different set of climatic conditions than glaciers in lower altitude mountains, such as in Norway or Sweden. For this reason, valley glaciers can have a range of thermal regimes, which control glacier flow, debris erosion and transport, and the creation of landforms.

The debris-covered Khumbu glacier in the ‘high-relief’ Everest region of Nepal. Notice the steep valley sides that rise far above the glacier and supply its surface with rock and sediment debris. Photo: Vlunyak

At a more local scale, topography (and especially relief) to a large extent determines how much debris is supplied to the glacier surface^1-3. For example, a valley with very steep sides is more likely to undergo regular mass movement (e.g. rock falls, landslides, slumps) that supply the glacier surface with rock and sediment debris than a valley with shallower sides.

Rockfalls and slumps from steep valley walls above Morteratschgletscher in the Swiss Alps. Photo: Samedan

Similarly, where there are large areas of rock exposed above the glacier, the chance of debris falling on to the ice surface is much greater than where there are very few exposed rocks on the valley walls that surround the glacier. Valleys with steep, high sides (that often rise >1000 m above the valley floor) are known as ‘high-relief’ areas, whereas valleys with less steep and lower sides are known as ‘low-relief’ areas.

Debris supply to glacier surfaces

As touched on above, the amount of debris covering a valley glacier surface can vary. Glaciers can be ‘clean’, meaning they have very little to no debris at the surface, or they can be ‘debris-covered’, where large areas (typically in the ablation zone) are completely mantled with rock and sediment debris.

Whether a glacier is ‘clean’ or debris-covered depends largely on how much and how often debris is supplied to the ice surface¹. As we have seen above, the glaciers of high-relief areas, such as the Himalayas, Andes, or Southern Alps of New Zealand, are surrounded by large, high, and very steep valley sides that release huge volumes of debris to glacier surfaces through rock falls, slumps and landslides⁴. Some mountain areas are also tectonically active. In these cases, earthquakes can trigger extremely large rock avalanches that run out on to glaciers in the valley bottom, significantly increasing the amount of debris at the ice surface^1,4.

The debris-covered tongue of the Tasman glacier in the Southern Alps of New Zealand. Photo

In other mountain areas – for example, where there is less exposed rock directly above a glacier’s surface, where the valley sides are less steep (and less prone to mass movement), or where the local geology is more resistant to failure and rockfall, the supply of debris to the glacier surface will be lower and the ice comparatively ‘clean’.

The largely ‘clean’ glacier surface of Nigardsbreen, western Norway. Photo: J. Bendle

How does debris cover influence glacier behaviour?

The amount of debris on the surface of a valley glacier can change its behaviour in several ways. First, it alters the glacier response to climate. Debris-covered glaciers have a muted response to climate (e.g. warming air temperature) as the debris that covers the ice surface (where thicker than several centimetres) insulates it against melting^1-3. For this reason, the terminus position of debris-covered valley glaciers is generally stable for long periods of time. ‘Clean’ glaciers, on the other hand, respond rapidly to climate with shifts in terminus position, as the insulating effect of debris cover is far less important.

The debris-covered snout of the Exploradores glacier in Patagonia (South America). Thick debris cover can slow the rate of ice-melt by insulating it from solar radiation. Photo: J. Bendle

Second, it alters the type of landforms that valley glaciers create. At debris-covered glaciers, huge volumes of debris build-up at the relatively stable ice margins, often leading to the deposition of large latero-frontal moraines^5,6. These moraines, in turn, influence the glacier response to climate, by providing a barrier to snout advance³.

Large latero-frontal moraines enclose the Mueller glacier, New Zealand, and its proglacial lake. Image: Google Earth (see below for a photo of the moraines).

Latero-frontal moraine of the Mueller glacier (see Google Earth image above) that rises around 80–100 m above the ice-front and proglacial lake. Large latero-frontal moraines like this form where valley sides release large volumes of debris to the glacier surface. Photo: K. Golik

At ‘clean’ glaciers, by contrast, there is less debris at the ice margin, and snout fluctuations mean that this debris may be ‘spread out’ across a larger area so that, in general, landforms such as moraines are smaller but more numerous (e.g. recessional moraines^7-9).

The amount of meltwater

The amount of meltwater flowing through a valley glacier is controlled by annual temperature and precipitation (and is therefore related to climate) and water storage in the catchment (e.g. does water move quickly through a glacier, or does it get stored in glacial lakes?)

Where sediment and rock debris are transported quickly through a glacier by large volumes of meltwater, a greater amount of glaciofluvial (e.g. outwash) landforms are formed^1,10 and the debris available to deposit moraines is reduced (leading to smaller moraines). These type of valley glaciers exist in humid mountain ranges that receive a lot of precipitation in a year. Examples include southern Chile, New Zealand, and Alaska.

Braided proglacial river network transporting meltwater and sediment away from the Tasman proglacial lake (New Zealand) and to form an outwash (sandur) plain. Photo: F. Rindler

By contrast, in colder, drier mountain areas, less meltwater is produced in a year and less sediment is washed away in proglacial streams. Therefore, debris transported to the glacier margins forms moraines, which can grow to be extremely large in size over time¹. This type of glacier tends to exist in high-altitude and arid mountain ranges, such as parts of the Andes and Himalayas.

The main types of valley glacier

As we have seen, there are many (interrelated) factors that influence valley glacier style and, in turn, the landsystems they create. To summarise, they can be divided into types¹ based on the amount of surface debris cover, with ‘clean’ and ‘debris-covered’ types, and based on the amount of meltwater they produce, where it is possible to have glaciers with efficient meltwater systems that wash large volumes of sediment from within the glacier and from around its margin, and glaciers with less efficient meltwater systems, where large volumes of debris can build up around their margins.

It is important to bear in mind that these four glacier types are ‘idealised’ examples. In reality, valley glaciers are extremely variable, as are the landforms and sediments they create. We will explore the various types of valley glacier and their landsystems further in this section of ‘AntarcticGlaciers’.

References

[1] Benn, D.I., Kirkbride, M.P., Owen, L.A. and Brazier, V., 2003. Glaciated valley landsystems. In Evans, D.J.A. (Ed.) Glacial landsystems, pp. 372-406.

[2] Benn, D.I. and Evans, D.J.A., 2010. Glaciers and glaciation. Routledge.

[3] Bennett, M.M. and Glasser, N.F.G., 2011. Glacial geology: ice sheets and landforms. John Wiley & Sons.

[4] Hambrey, M.J., Quincey, D.J., Glasser, N.F., Reynolds, J.M., Richardson, S.J. and Clemmens, S., 2008. Sedimentological, geomorphological and dynamic context of debris-mantled glaciers, Mount Everest (Sagarmatha) region, Nepal. Quaternary Science Reviews, 27(25-26), 2361-2389.

[5] Boulton, G.S. and Eyles, N., 1979. Sedimentation by valley glaciers: a model and genetic classification. Moraines and varves, 33, 11-23.

[6] Benn, D.I. and Owen, L.A., 2002. Himalayan glacial sedimentary environments: a framework for reconstructing and dating the former extent of glaciers in high mountains. Quaternary International, 97, 3-25.

[7] Matthews, J.A., 2005. ‘Little Ice Age’ glacier variations in Jotunheimen, southern Norway: a study in regionally controlled lichenometric dating of recessional moraines with implications for climate and lichen growth rates. The Holocene, 15(1), 1-19.

[8] Beedle, M.J., Menounos, B., Luckman, B.H. and Wheate, R., 2009. Annual push moraines as climate proxy. Geophysical Research Letters, 36(20).

[9] Lukas, S., 2012. Processes of annual moraine formation at a temperate alpine valley glacier: insights into glacier dynamics and climatic controls. Boreas, 41(3), 463-480.

[10] Kirkbride, M.P., 2000. Ice-marginal geomorphology and Holocene expansion of debris-covered Tasman Glacier. New Zealand, IAHS-AISH P, 264, pp. 211-217.