The first Alaskan glacier I went to was Portage Glacier. This one can be found on the Kenai Peninsula, not far from Anchorage and is unique in that it flows into a lake (Portage Lake). You can take a boat out on the lake to get up close to the glacier. It was a cold, wet and bleak day during my visit. Kind of seemed appropriate for visiting a frozen natural wonder.
Glaciers form over great periods of time where ever snow falls faster than it melts. The snow builds up and turns to ice. The ice then slowly but surely deforms and moves due to the weight of the snow and ice above it. This is when it becomes a glacier and over time these ice fields form into what looks like a frozen river flowing over a mountain or through a high valley.
The deeper the ice the more blue a glacier looks too. When white light hits the surface it reflects quickly back on snow that is not very thick to give you the white colour (this is caused by red light which is the long wavelengths of white light), but thick ice takes longer for light to penetrate and it become more scattered which in turn gives a blue effect (this is caused by blue light which is the short wave lengths of white light).
The US National Park Service says that most of the glaciers in Alaska are less than 100 years old and a good estimate on the depth of one is about half the surface width of the glacier. Sadly many are retreating glaciers today.
According to the US Geological Survey (USGS) there are 600 officially named glaciers in Alaska but there are far more than this in that huge state. The US National Parks Service indicates that the Alaskan Almanac count of 100,000 glaciers in Alaska is a pretty good estimate. During my trip in Alaska I barely scratched the surface. The mind boggles!
The Portage Glacier once extended 23 kilometres / 14 miles through the Portage Valley. A visitor centre was built in 1986 to view the glacier. Today you apparently cannot even see it from there (I did not visit the centre) and hence you take a boat ride out to view the glacier now. Sadly the glacier and its ice flow has retreated significantly in the past 50 plus years. Still a spectacular sight but our impact on the earth is obvious. Lets hope we can change that someday.