At Old Volcanoes, Slopes Turn Mudflows Deadly

BUFFALO, N.Y. -- Mudflows initiated by natural processes at old, inactive volcanoes are some of the most lethal geologic phenomena and they contributed to last week's tragic mudslide in Guinsaugon, Philippines, according to a University at Buffalo scientist whose team has developed advanced computer models of mudflows.

"They really come roaring down, like the speed of these toboggans you see on the Olympics," said Michael F. Sheridan, Ph.D., professor of geology in the UB College of Arts and Sciences and director of the geology department's Center for Geohazards. "The mud looks like liquid chocolate pouring down the valley and the rocks they contain behave like marshmallows in hot cocoa, so big rocks can be brought downhill very fast. The flowing material is much denser than water, so it transports the buoyant rocks very quickly."

Sheridan explained that fresh volcanic rock can be quite stable, forming steep cliffs on active volcanoes.

"However, over time, weathering can change the rock to clays or soils that are only stable on gentle slopes," he said. This material has a tendency to slump in a landslide in order to maintain its equilibrium and this process doesn't occur on a grain-by-grain basis, but rather in one big step."

When that process is provoked by heavy rainfall, he added, as was the case in the Philippines, the potential for tragedy is nearly unavoidable.

"Mudflows are the volcanic phenomena posing the greatest danger to populations," he said, noting that in 1985, a volcanic mudflow in Colombia killed 26,000 people.

The National Science Foundation sent Sheridan to Nicaragua in 1998 to conduct research at Casita volcano, where mudflows associated with Hurricane Mitch killed more than 2,400 people.

He said there are similarities between Casita's mudslide and last week's in the Philippines.

"Both mudslides were generated by heavy rainfall in areas prone to previous landslides," he said, "and in both cases, the initial slide transformed into a mudflow that was much more mobile and spread across a greater area."

He added that unlike lava flows, which generally travel less than a mile per day, mudflows move extremely fast. A mudflow last February at Ecuador's towering Tungurahua volcano that he studied moved at speeds of up 20 feet per second and some mudflows can move twice as quickly (see animation at story link at top of page).

He noted that mudflows at old volcanoes especially are dangerous because volcanoes have steeper topography due to erosion and because the combination of percolating water and acid from the leaking volcanic gases generally converts volcanic rocks into clay, which is very unstable and extremely slippery.

Sheridan's team, funded by the National Science Foundation, has developed the TITAN code, one of very few computer models that incorporate the underlying physics of the flows to simulate volcanic phenomena, including mudflows.

According to Sheridan, it is the range in the viscosity of such flows that makes these simulations so difficult.

"Viscosity of these flows encompasses the whole spectrum of behavior, from that of completely dry materials to completely wet and everything in between," he said. "Once you've got a 50-50 mix, you've got a debris flow and that's what's really dangerous."

The UB group, which includes mathematicians, geologists, geographers, computational scientists and mechanical and aerospace engineers, is one of the most multidisciplinary -- and ambitious -- teams in the world working on computer models for volcanic hazard mitigation.

Currently, with NSF funding, the group is conducting research modeling mudflows with other research groups located in Mexico, Costa Rica, Ecuador, France, New Zealand and Spain.

In New Zealand, they are working with geoscientists at Massey University to model the movement of potential mudflows on Mt. Ruapehu, where a crater lake is filling with water and a mudflows hazard has been forecast. The UB scientists are using remote devices placed in the stream bed to measure velocities, densities and water content of mudflows there that they will incorporate into their TITAN models to produce more precise simulations.

In one calculation, the UB scientists determined that a large mudflow near Colima, a major volcano in Mexico, could consist of a wall of water and debris 200 feet high.

Sheridan noted that it may seem that mudflows are occurring more frequently than in the past, such as last year's lethal mudflows in Conchita, Calif., and the recent one in the Philippines. The increase in deaths from such events, he said, is more likely a result of global population shifts.

"In California, for example, more people are building homes on the hillsides, causing the slopes to become steeper and creating increased mudflow potential," he said.

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