The Mendenhall Ice Cave was (or is) a glacier cave, a cavity within the Mendenhall Glacier.
There have been several different Mendenhall Ice Caves.
When it is warm enough, water runs through cracks in the surface of the glacier.
Eventually, the water may create a large tunnel. Where the water leaves the cave, may be able to walk in.
Sometimes it make take more effort.
Exploring a exposed glacier tube that, at one time, transported water down the glacier. Its fractured remains are seen here thrust up in a tension zone on the Mendenhall Glacier.
Tongass National Forest, Juneau Ranger District, October 2017.
Forest Service photo by Adam DiPietro.
Icicles look somewhat like stalactites.
Why is the Mendenhall Ice Cave blue?
The ice is blue for the same reason the sky is blue. All of the other colors in the spectrum of visible light are absorbed. Only blue is bounced back for our eyes to see.
Glacial Caves can be dangerous. They can collapse.
The Mendenhall Glacier moves. Melt water continues to enlarge the cavity, so eventually caves in the Mendenhall Glacier collapse and vanish. Right now, in 2019, there are no caves in the Mendenhall Glacier, but by the time you are reading this, there may be one again.
The Mendenhall Glacier is in the Tongass National Forest, where there are also a lot of sinkholes and karst caves. Two caves are open to visitors, El Capitan Cave and Cavern Lake Cave.
You can wade into Cavern Lake Cave to the end, only about 55 yards.
El Capitan Cave is the longest mapped cave in Alaska. The park has a two-hour tour into the cave. You have to reserve ahead of time, wear appropriate footwear and bring your own flashlights and batteries. The Forest Service provides hardhats.
Photo at top of page by Kenneth J. Gill