Glacial Movement Resulting in the Discovery of Ice Mummies

Glaciers

From the frigid lands of Greenland and Antarctica to rising mountain ranges such as the Andes and the Alps, glaciers lie within many of these frozen landscapes.  Approximately 10% of the earth's land surface is currently covered by glaciers, however, during the past ice ages they covered about three times as much (1). The map on the left shows the areas of glaciers in the world.  It is interesting to see that even in warm climates such as South America and Africa, alpine glaciers can exist in the high mountainous regions.

Map source

Glacial Anatomy

Glaciers are formed in areas where low temperatures and high amounts of snowfall are consistent (2). This snow accumulates and packs together, creating a solid body of firn. Eventually, as more snow falls and condenses, the weight created causes the firn to become more dense and impermeable, and over a few years this process creates glacial ice ( 3 ).  However, because of the fairly constant accumulation of snow, firn continues to develop on top of the glacial ice.  This firn keeps changing form into glacial ice and that is why glaciers can become over several kilometres thick (4). 
As seen in the alpine glacier diagram to the right, a firn limit exists between the zone of accumulation and ablation.  The accumulation zone is where the majority of snow accumulates and therefore firn develops.  This is represented in the diagram by the white layer in the zone of accumulation.  However, past the firn limit is the zone of ablation.  In the ablation zone, snow and firn is lost through melting and therefore the surface consists of exposed glacial ice.  The process of accumulation and ablation maintains mass balance creating a state of equilibrium for the glacier.  If more snow accumulates one year, then an increase of ablation will follow, but might not occur for a few years depending on the rate of which the glacier is moving.   For Glossary.                                                                             Diagram Source      

On the left below is a photograph of a glacier. This photograph is labelled with the firn line which is quite visible at the end of the ablation season ( 5 ). Below on the right is a diagram of a glacier which shows the firn line and the equilibrium line.  Above the equilibrium line is the zone of accumulation, and below is the zone of ablation (same as firn line) however the equilibrium line refers to the process of mass balance rather than the presence of firn.(6).

                             

Source: left diagram
Source: right diagram

Because of the fact that the glacier ice is so thick, a lot of pressure is created near the bottom which causes the glacier to become plasticized and it begins to move (7).  Movement is the key characteristic of a glacier; whether the glacier is in the process moving, or has moved in the past (8). However, the response to pressure results in different types of movement between alpine and continental glaciers. Continental glaciers tend to expand outward while the alpine glaciers tend to move down the slopes of the mountain (9).  Alpine glaciers move in constant motion flowing from higher points of elevation to the lower areas.  An important thing to remember is that these alpine glaciers can advance and recede at the toe, but the ice is constantly moving forward.  The more pressure a glacier experiences, the faster it moves.  Furthermore, different speeds of movement are found within the glacier. The diagram on the left ( 10 ), shows the flow pattern of the glacier, and the point at which the ice flows faster.  The ice on the outside edges of the glaciers moves slower because of the resistance caused by the land material ( 11 ).  For example, if the glacier were to flow through a valley, the resistance caused by the sides of the valley walls would slow down the outside of the glacier. Therefore the center moves faster.  In the diagram, this is shown by the fact that the rocks in the center have moved farther ahead than the others.  However, the speed of glacial movement also changes within the horizontal layers of the glacier.  The diagram on the right ( 12 ), shows a vertical cross-section of a glacier.  The bedrock base causes resistance for the flowing ice, therefore, the flow of ice is slower near the bottom of the glacier.  The red arrows depict various layers of ice that move at different rates of speed.  The bottom layer is the slowest and the layers increase in speed towards the top.  Each layer is carried along by the one below and since the upper layers are moving away from the resistance of the bottom, they move faster than the layer below (13). Also, in the area between the head and the toe, basically at the equilibrium line, the glacial ice moves faster. This occurs because the pressure created from the amount of snow, firn and glacial ice in the accumulation zone, creates more stress and therefore causes the ice to move faster (14).  However, the ice slows down after reaching the ablation zone because melting occurs and therefore less pressure is created (15).   Therefore, the ice of a glacier moves the fastest at the surface, in the center (between the left and right sides), at the equilibrium line.

It occurs at any temperature of ice although is most effective in higher temperatures (19). This process does not involve sliding, but flowing ice, which moves around obstacles (20).  Any material protruding into the base of the glacier, such as a boulder, causes more strain on the ice and therefore leads to an increase of velocity (21).  The bigger the obstacle, the more the velocity increases.  This type of flow is not only the main form of ice flow at the bottom of the glacier, but it also directs the flow of the ice (22).

Another process related to glacial movement is pressure melting. This process occurs in warm glaciers and involves pressure build up, which results in melting (23).   As shown in the diagram on the right, this occurs when the ice moves over small bumps in the bedrock below.  As the glacier ice moves up the side of the bump, melting occurs because of the pressure forced upon it (24). The water that is produced from the melting, then flows over the downward side of the bump where the pressure is lower and the water refreezes (25).  This refrozen ice is called regelation ice (26).  The obstacle size has a crucial role in how effective this type of movement can be.  If the size of the obstacle is less than one metre, than the ice can move around it more quickly, but a bigger obstacle will slow down the process (27).  

Slippage over a water layer is another example of a process resulting in glacier movement.  This process occurs in a warm glacier where a thin layer of water exists between the bottom of the glacier and the bedrock.  The water may only be a couple of milimeters deep but this can account for up to 90% of glacial movement (28).  This accumulates from sources such as melting within the galcier, rain water or groundwater.  This water can not be completely compressed by the glacier and that is why the glacier can flow on top of the water (29).  As well, slippage can also occur as the glacier moves over till, or loose unconsolidated material, which acts somewhat like marbles and allows the glacier to slide over the surface (30).

A kinematic wave is basically a bulge of increased thickness of ice that is caused by a high amount of accumulation in a season ( 31 )

 

As you can see, glacier movement is a very complex system, made up of many different features.  Glacier movement can increase or decrease due to various aspects such as different climates, slopes and debris content.  Furthermore, this movement can create unique erosional features that can be left behind for thousands of years (For erosional features see: http://www.uwsp.edu/geo/faculty/ritter/geog101/lectures/lecture_glacial_processes.html ). However, with regards to the process of glacier movement, erosional features may not be the only things left behind. These processes have been known to reveal some shocking discoveries...
Unfortunately glaciers are quite hazardous to humans as people travelling over them can fall in the large crevasses which may result in death. Over the centuries, the movement of the glaciers causes these bodies to emerge from the ice and become exposed in the ablation zone as the ice melts. Therefore, bodies that are thousands of years old can be found and may be used to provide answers about our history.



Ice Mummies

The frozen bodies found due to glacial movement and ablation, are known as ice mummies.  Some of these findings can date back to the periods of early man. These findings range in location from all over the world, and because of the amazing preservation from the ice,they present fascinating information from earlier periods in time.  (For information about how the ice preserves the bodies go to: http://www.howstuffworks.com/question712.htm.

August of 1999, sheep hunters in British Columbia discovered a body on the slopes of a melting glacier in Tatshenshini-Alsek Provincial Wilderness Park ( 37 ).  Kwaday Dan Sinchi, as the body was named, was in fact from the fifteenth century ( 38

). The photograph on the right is men working to extract Kwaday Dan Sinchi's body from the ice (39 ). Similarly, “Ötzi the Iceman” was also discovered in a melting glacier in September of 1991 ( 40 ). Otzi (photograph on the left) was found near Hauslabjoch in the Ötzal Alps, however, unlike the more recent Kwaday Dan Sinchi, Ötzi died approximately 5200 years ago ( 41 ).  The photograph to the lower right shows the medical experts observing this amazing find (42 ). The hunt to find out who Otzi was has led to many theories about how he died which can be found on this site: http://www.d.umn.edu/cla/faculty/troufs/anth1602/pcice_man.html