Glaciers / Glacial Features
Ice has been a major force in the Glacier Bay region for at least the last seven million years. The glaciers seen here today are remnants of a general ice advance – the Little Ice Age – that began about 4,000 years ago. True to its name, this advance in no way approached the extent of continental glaciation during Pleistocene times known as the Wisconsin Ice Age. The Little Ice Age reached its maximum extent here about 1750, when general melting began.
The advance or retreat of a glacier snout reflects many factors: snowfall rate, topography, and climate trends. Most glaciers in every mountain range and island group in Alaska are experiencing significant retreat, thinning or stagnation. Today, glacial retreat continues on the bay's east and southwest sides, but on the west side several glaciers are actually stable or advancing, fed by copious snowfall high in Fairweather Mountains.
What is a Glacier?
Glacier ice is different from the ice in your refrigerator. The ice crystals form slowly under pressure and individual crystals can grow to be the size of a football. Air trapped between the snowflakes is also frozen into the ice at pressure. Ice near the bottom of the glacier is under tremendous pressure, which allows it to flow almost like a plastic over the bedrock beneath. Friction between the glacier and the bedrock produces meltwater which further lubricates the bedrock allowing the ice to slide.
Colors betray a berg's nature or origin. White bergs hold many trapped air bubbles. Blue bergs are dense and are likely recently calved. Greenish-blackish bergs may have calved off glacier bottoms. Dark-striped brown bergs carry morainal rubble – rocks that the glacier acquired on its journey down the mountain.
How high a berg floats depends upon its size, the ice's density, and the water's density. Bergs may be weighed down or even submerged by rock and rubble. A modest-looking berg may suddenly loom enormous – and endanger small craft – when it rolls over. Boaters and especially kayakers should keep in mind that what one sees is "just the tip of the iceberg."
Glaciers of Glacier Bay
Repeat Photography of Glacier Bay's Glaciers
Glossary of Glacier Terminology
Anatomy of a Glacier
A Changing World