Scientists say the deformity is caused by pressure from magma that is fitfully working its way toward the surface and a probable eruption. They say all the events of the last two weeks — earthquakes, harmonic tremors, ash explosions and steaming inside the crater — are likely leading up to such an event.

Originally posted by HarmoniusOne
However, if you look at the activity over the past week or so, some show shakes when MSH is active, some when she's quiet. Mt Constitution never even hiccupped through all of this and then yesterday started shaking and hasn't stopped.

An interesting variation of a composite volcano can be seen at Crater Lake in Oregon. From what geologists can interpret of its past, a high volcano -- called Mount Mazama -- probably similar in appearance to present-day Mount Rainier was once located at this spot...

"What's happened in the last day is the magma is not just pushing up but pushing out. We no longer have just isolated vents. Instead the whole area is pushing up, the gas is the fuse, just oozing out," John Pallister, a U.S. Geological Survey geologist, said at a news conference yesterday afternoon.

Fast-moving magma would cause greater concern because explosive gases wouldn't have time to dissipate. A team in Denver is evaluating air photos, comparing pictures of the changing lava dome to gauge how fast the magma is rising.

"Rapid ascent is very dangerous, whereas if it rises slowly the magma has a chance to degas and then it would just ease its way out," Pallister said.