Jon Major, a hydrologist for the U.S. Geological Survey, holds a picture showing the glacier 'donut' inside the Mount St. Helens crater.

VANCOUVER, Wash. – A new formation inside the Mount St. Helens crater is fascinating both scientists and tourists. It has also a strange nickname – the donut.

The mountain's second lava dome pushed up and through the original glacier. As it grew, it pushed the split glacier forward toward the crater's mouth until it finally rejoined – completing a circle of ice on the crater floor.

"In the lower 48 states, this is one of the few glaciers that's actually advancing," said Jon Major, a hydrologist for the U.S. Geological Survey. "All the other glaciers in the Cascades are retreating."

The question for scientists is whether the glacier will continue pushing forward – perhaps onto the valley floor itself.

"Is it going to make it all the way to the gully systems that, you know, spill out of the crater?" Major asked. "Will it actually advance out of the crater?  Or will it now stabilize where it is and begin to retreat?"

And now that the lava dome eruption has stopped, scientists wonder if the glacier's growth will slow down or stop too.