Georgia correspondent Daryl Weinhoff is blogging about her study abroad experience in New Zealand this summer.
Although the general pattern since the 1800s is for most glaciers to retreat, New Zealand's Fox Glacier is actually advancing. According to Coates, this pattern has been evident by "the latest advance of the 80s and 90s." In order for a glacier to be balanced, there needs to be a relatively equal amount of snow accumulation in the top part of the glacier and ice lost in the lower glacier. The result of an unevenly balanced glacier will either be advancement or retreat.
The advance and retreat of glaciers is typically caused by one of two factors: climate change or change in precipitation. The changing of climate to cooler temperatures causes advancement due to the same reason glaciers formed in the first place. Coates states that "as moisture-laden winds and frequent storms climb the mountains, the air cools rapidly causing heavy ran and snowfalls." This snow is then packed down and turns to ice. Retreat is caused when there is an increase in temperature, and therefore leads to melting. However, temperatures can go down and glaciers can retreat due to reduced snowfall.
Even though the slight advance or retreat of a glacier is not enough to prove or disprove global warming theories, it can provide assistance in explaining the ongoing trends. The retreat of glaciers started to occur when there was an unmasked increase in temperature. This supports the ideas of global warming seen through "the overall retreat of these two glaciers in this century has been punctuated by minor advances at about 20-year intervals" (Coates 1999).
Photos: Daryl Weinhoff