Waiting for Redoubt's big boom

The clock is ticking for the new dome growing at Redoubt to collapse. What will happen if/when it does collapse? Good question!

The new dome at Redoubt. Image courtesy of AVO/USGS, taken by Game McGimsey, April 30, 2009.

Most likely, the following will occur:

First, extrusion of lava will cause the dome to over-steepen, precipitating the collapse (although a large seismic event could also trigger collapse as well). An excellent example of this is the spine that grew at Mont Pelee on Martinique in 1902 before the famous eruption that destroyed St. Pierre and killed >30,000 people.

When it cannot hold itself up anymore, the dome will crumble gravitationally.

As the rock breaks away and moves downslope, the pressure on the underlying hot magma will lessen and cause an explosive component to the eruption.

If directed upward, the explosive component will produce a subplinian-to-plinian ash column (up to 10 km / 30,000 feet according to AVO).

The hot material of the dome that moves downslope will produce a pyroclastic flow, specifically what is known as a “block & ash flow“. Here is a brief video of one from the dome collapse at Soufriere Hills, Montserrat.

This hot pyroclastic flow (or nuee ardente) will melt snow/ice on Redoubt and mix with runoff to form lahars that will travel down the drainages on the edifice, possibly all the way out to the inlet.

Generation of pyroclastic flows from dome collapse. Figure courtesy of the USGS.

Impressive, eh? Of course, it might not happen exactly like this. There are many variable (extent of collapse, pressure from underlying magma, magnitude of pyroclastic flows generated and many others), but more than likely, block & ash flows and lahars will be generated when the dome does collapse.

The latest from AVO suggests they think it will happen soon and without much warning, so keep an eye on the webcams (DFR and Hut).