Glacial Processes
In the simplest respect, glacial processes created Fiordland and Milford. This however does not give a very clear or concise answer as to how. To understand the formation one must first understand glacial processes. The definition of a glacier is “A slowly moving mass of dense ice formed by the gradual thickening, compaction, and recrystalization of snow and water over time (Arbogast, 2007).” Over time snow and other forms of frozen precipitation fall, in this case, in an alpine region. The snow then compacts over time as more and more precipitation falls on top of it year by year. Eventually this compaction forces the ice crystals to rearrange themselves to make a solid substance know as firn. At this point the firn turns to ice and starts is descent down the mountainside.
It is important to know about the different zones that exist on a glacier. In total three different zones make up the entirety of a glacier (Fig. 1)
Fig. showing three different zone of a glacier
The Zone of Accumulation is an “area where snow accumulates and feeds growth.” The Zone of Ablation is an “area where glacial melting exceeds accumulation.” The Equilibrium Line is “the place on a glacier where snow accumulation and melting are in balance (Arbogast, 2007).” Above the Equilibrium line, the total amount of precipitation continues to increase due to a lack of melting in this area. Below the line, the accumulation cannot keep up with the total amount of melting that occurs. Depending on the climate and precipitation in any given year, the glacier can either grow or recede up or down the mountain.
In the case of Fiordland, alpine glaciers are the tools at work that carved out all the fiords and lakes within the park. As the snow accumulates high up in the mountain, in this case the Southern Alps, a mass of ice starts to form and grow in size. Eventually this ice mass will start to experience the force of gravity because of is considerable size and mass. This ice mass is then considered to be a glacier because of the movement that is caused by gravity and the downhill slope of the mountain. For the most part these types of glaciers tend to flow down V shaped valleys formed by fluvial processes. As the glacier starts to creep down the mountain, its mass is so huge and the gravity is so great, that it starts to eat away at valley.
Over many thousand of years, the glacier eats and scrapes away, through different types of erosional processes, at the V shaped fluvial valley until it starts to recede. Abrasion and plucking are probably the two biggest forms of a erosion that take place during glaciation. Abrasion occurs when the bottom of the glacier slowly collects little stones and pebbles, which are then used to grind away at the bedrock. Plucking is a different type of erosion. Through this process, the ice as it passes overhead can get into the cracks of the ice and literally pluck bits and pieces off of the bedrock. All of these processes occur until there is finally a recession in the movement of the glacier.
The glacier can recede for a variety of reasons. In most cases, the general climate changes in a specific location that can completely change the equilibrium of the glacier. If the climate were to warm up then the glacier would begin to melt away. It starts to recede back up the valley it resided in for some many years. In its wake, there is a new valley formed. Arbogast states, “The pre-existing V-shaped valley forms into a U-shaped valley called a glacial trough (Arbogast, 2007).” The valley is a very common alpine feature. In the case of Fiordland, all of the alpine glaciers that developed were considered Tidewater glaciers. “Tidewater glaciers occur where glacier ice meets the sea (Arbogast, 2007 Fig 17.10). Once the glacier melts away, the U-shaped that formed in its wake is gradually filled in by water as sea level begins to rise. The only thing that remains in its wake is the high walls of the U-shaped valley that was not covered or drowned by water. Today the most common name for this remnant is a fiord. A fiord according to Arbogast is “A former glaciated valley along the coast that is flooded by rising sea level (Arbogast, 2007).” Through the course of history, these areas are popular vacation destinations and places of rich biodiversity.