 Photo showing the Mendenhall Ice Cave in Juneau, AK. Date unknown (Travel Magazine). When you think of ice caves, you might think of a scene out of frozen – glittering blue ice that reflects off the sunlight. Some famous ice caves include Kamchatka Ice Cave in Russia, the Ice Grotto of Mittelallalin (part of the Fairy Glacier in Switzerland), the Big Four Ice Caves- part of Mount Rainier WA, Bandera Ice Cave and Volcano outside of Grants NM, and the Mendenhall Ice Caves & Glacier in Juneau Alaska. The Mendenhall Glacier is a 12-mile long glacier in the Mendenhall Valley and only 12 miles from downtown Juneau in southeast Alaska. The glacier originally went by its Native Tlingit names Sitaantaagu (“Glacier Behind the Town”) and Aak’wtaaksit (“Glacier Behind the Little Lake”), which literally encapsulates the city of Juneau. On rare summer days, it can be a pleasantly warm summer day in Southeast Alaska, with temperatures stretching near 80. And yet, a spectacular cathedral of ice lies behind the glacier. Ice stalactites stretch down from the ceiling towards ice stalagmites stretching up from the floor. What lies below is a delicate balance. Generally, the caves form by meltwater streams carving labyrinths in the base of the glacier, or in other cases the wind hollowing out tunnels in snowfields. The melting water constantly creates new caves. Over time, the main cave may collapse from the shifting and retreat of the glacier. Inside the glacier lies stunning blue ice caves, accessible to those willing to hike to the backside of the glacier, kayak to the edge of the ice, or walk across the frozen Mendenhall Lake during the wintertime. The blue ice coming from compacted snow – the air bubbles are squeezed out and makes the ice appear blue. These constant forces, fast-moving streams, and falling rock can make the ice caves unstable and dangerous at times. However, the caves tend to maintain a constant temperature year-round. One theory to why ice caves form is the “cold source” theory – suggesting that there is a local reversal of geothermal heat from the Earth’s hot mantle that may miss a particular patch, leading to icy deposits in the cave. It turns out that the combination of the cave’s particular shape and position, the seasonal flow of air through the space, and the nature of the heat exchange with the walls creates a unique micro-environment necessary to keep the cave ice cold, even when the outside world is warm. Once ice forms in a cave, it acts as a buffer that stabilizes the temperature. If warmer air passes through the cave, the ice may begin to melt. But, melting takes a lot of energy, so that little meltwater is absorbed and prevents the cave from warming up too much. In addition, when cold air funnels in, any liquid water in the cave will freeze, releasing latent heat energy, and stabilizing the temperature inside the cave. Some ice caves have more than one entrance, which affects the seasonal air flow and the extent the ice melts and re-grows each year. If the entrances also open at different heights, it encourages even more flow of cold air through the cave (Science Explorer). The caves aren’t simply a tourist attraction, but they can be important archives of past atmospheric and environmental conditions. The gas bubbles trapped in the ice can shed some light on the ancient composition of the atmosphere at the time it froze, the temperature of the caves and how it changes with time, and how the wind currents shape the walls of the ice cave. Unfortunately, ice caves such as the Mendenhall, are in danger due to rising temperatures. The ability for the caves to maintain a constant temperature may lead to the development of a new form of air conditioning for buildings (such as how a basement traps cold air), which is important in a changing climate. To learn more about geoscience topics, please click here! © 2022 Meteorologist Sharon Sullivan References:
Some photos the author took during her visit to the Mendenhall Ice Caves on Feb 5, 2018.
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