Glaciers are non-homogenous natural bodies composed of ice. They are part of the hydrosphere and the cryosphere. Their study occupies the science known as glaciology. Mostly a glacier is in the shape of a loaf of bread or a tongue. Glaciers are formed from an accumulation of snow that under the influence of its surroundings is converted to névé, from névé to firn, and from firn to glacial ice. The process of transformation from snow to firn is called nivation. This is caused primarily by thawing and repeated freezing under pressure from higher layers of snow, but it can also result from temperature changes. This process of thawing and freezing is called regelation. This feature makes the glacier into a malleable body capable of filling and modelling the relief of the earth. Glaciers occur on all continents with the exception of Australia. Glaciers have a so-called “accumulation zone”, in which the accumulation of snow takes place, and an ablation zone, in which the melting away of the glacier takes place. Both zones are separated from each other by an imaginary line of balance above which accumulation takes place and below which ablation takes place.
Glaciers are divided into two groups:
- continental (e.g. Antarctica, Greenland)
- mountain (e.g. in the Alps)
In mountaineering we most often encounter mountain glaciers.
Types of mountain glaciers
Mountain glaciers occur in a number of types:
Found on a flat mountain tract (plateau), tongues of which leak out into multiple directions. (e.g. the Halls tatter Glacier in Dickstein).
These are found in a cirque and have nowhere to flow. They are like a lake enclosed by cliffs, except made of ice instead of water.
A kind of glacier which has flowed to the edge of a large precipice in the terrain, from whose front section large slabs of ice will break off and plummet down the mountain flank with the next downward movement. Oftentimes entire icefalls can occur full of sera’s (glacial blocks, towers) which connect a hanging glacier with a valley glacier. It can also happen that the slabs of ice from a hanging glacier hurtle downward into a dry valley as an ice avalanche. And there they melt.
A glacier which is flowing through a mountain valley and is similar to a river. It is actually a long glacial tongue sliding slowly forward.
A glacier moves at a speed of roughly 20-300 m per year. The thickness of the glacial layers can vary, but in certain places they can be as thick as 300 m.
Glaciers occur via snowfall. In high mountain locations layers of snow fall such that the bottom layers of snow are compressed due to the constant fluctuation of temperatures and pressures; snowflakes lose their crystalline structure, and at first glacial firn forms (very coarse grain snow) and from this glacial ice. Due to its incredible size, its mass begins to flow along the path of least gravitational resistance – downward. The ice of a glacier is coarse-grained, and is permeated by a multitude of small air bubbles. In places with colder climates, snow or firn accrues on the surface of the glacier. In lower locations, where it is warmer during the day, the surface of a glacier is formed of coarse-grained ice.
We can observe a multitude of formations and phenomena on a glacier. The greatest role played by any of these for mountaineering is that of glacier crevasses.
We can identify several types of crevasses based on their general location in the glacier (e.g. longitudinal crevasse, transverse crevasse, etc.), and then according to the profile of the crevasse (e.g. “A”, “V”).
Found at the upper edge of a glacier. Caused by the tearing free of a glacial mass from a firn bank on a hill. In the bank no large layers of snow are formed (because of the slope, new snow slides downward immediately after falling, as do the various shifts of snow and small snowslides), and therefore the thinner and lighter firn snow does not have such a tendency to slide downward. On the contrary, a lower placed, heavy and voluminous glacier does. The glacier therefore tears free of the firn field and a Bergschrund crevasse is formed.
This often presents a complicated spot when ascending a mountain face, the same way a moat defends against approach under a castle wall.
This runs parallel to the direction of flow of the glacier. It occurs either in spots where the bed of the glacier is expanding, or over terrain irregularities of the subsurface at the bottom of a glacier whose course matches the direction of flow of the glacier.
Longitudinal crevasses also form on the inner side of the turn of a valley glacier, where these crevasses are not wide, rather they are little cracks, but the individual blocks of ice are shifting up and down against each other. This is caused by the higher pressure in the ice in these spots.
Occurs in spots where the subsurface under the glacier is either dropping, or is becoming more gradual; always, however, this terrain irregularity is perpendicular to the direction of flow of the glacier. Transverse crevasses are most frequently formed in two profiles, “V-shaped” and “A-shaped”.
Occurs in spots of terrain elevation (bulges). The crevasse narrows as it deepens. The fact that it is wider toward the surface can be easily seen from a distance, and for this reason it does not pose too great a danger. As a rule we can go around it. If, however, it lies in our way and cannot be circumvented, it can be very difficult to get past. We must carry out reconnaissance and find a spot where it is possible to descend into it and ascend out of it on the other side. In such a case a person cannot avoid ice climbing, and therefore such an approach requires the necessary gear.
Occurs in recesses and expands as it deepens. Often only narrow clefts of the crevasse can be seen on the surface, which are covered by snow bridges. While these enable us to cross the crevasse, at the same time there is a risk of falling through them. To travel in such terrain without protection is sheer suicide.
Occurs at the spot where the glacier and the rock meet. Due to how the sun shines on the rock during the day, the rock warms up – far more than the mass of ice. The glacier therefore thaws at this point, gradually melts away and thereby the randkluft crevasse occurs. It can often be very wide and deep.
Forms due to a difference in speed of flow of the glacier. It has a slanting direction when compared to the direction of flow of the glacier. In the middle of the glacier the ice flows more rapidly, whereas at the edges it flows more slowly, since it is held back by friction against the surrounding rock. The faster centre is thus essentially “escaping” the edges, and strain occurs between both sections of the glacier which leads toward cracking of the ice. Crevasses formed in this manner are perpendicular in the direction of strain; that is, they are predominantly directed perpendicular to the edge of the glacier upward (“against the current”) toward the centre of the glacier. They are wider at the edges and grow narrower in the direction toward the centre of the glacier.
This is shown in detail in the figure. In the centre of the glacier (a) the current of flowing ice is faster than the edges (b), where it is slowed by friction against the rocky bank. In the same amount of time, the two points A and B set off from the first position to the second position at various distances, by which both points have grown further apart; strain arises in the ice between them, thereby causing crevasses.
Found at the front of a glacier flowing out of a valley, where the glacier spills out into width. It is actually a longitudinal crevasse (because it progresses in the direction of flow of the glacier), but at the same time multiple radial crevasses lie radially askew to each other.
Under the glacier a large rocky hump can be found, and the glacier on top of it bulges upward. In this way a glacial hump occurs, which is often churned up by V-shaped crevasses and which lie oriented toward each other either in the shape of an X (an X-shaped crevasse), or which are radially branched in a direction away from the middle of the hump. In places where the glacier has a sharp drop downward, an icefall can occur. A glacier in such a location significantly fragments into various ice blocks and towers, and a ready-made ice labyrinth occurs. These ice blocks are called seracs.
Crevasses are sometimes covered by fallen or windswept snow. In this way snow bridges are formed. Sometimes a bridge is formed across a crevasse because a serac has fallen and becomes wedged in the crevasse.
In warm summer days, often various channels or streams of water will flow along the surface of a valley glacier. In appropriate spots the water (and the stones which the water carries with it) can wear a path through into the core of the glacier. A crater of sorts is formed, into which the stream disappears; these are called moulins. Water then leaks from the front of the glacier via a glacier cave. With its movement a glacier significantly shapes its rocky surroundings. It pushes an abundance of rock and stone ahead of it. This forms terminal moraines. Rocks accumulate, particularly with valley glaciers, along the sides of the glacier as well; this leads to the creation of lateral moraines. If two glaciers flow into each other, the stones from the rocky promontory between them are carried away into the middle of the new, conjoined glacier, and medial moraines are thereby formed.
This content is preview from e-book.
Mountaineering Methodology – Part 4 – The Mountains
Available for download from Apple iTunes (in the Books section).
For example U.S. store – link
Another countries – look on the page Download
Another possibility is Google Play. This version is a simplified (as PDF).
Mountaineering Methodology – Part 4 – The Mountains
Available for download from Google Play.