Carleton prof sheds light on erupting volcanoes
Two global volcanoes erupt one month apart. El Fuego in Guatemala kills dozens of people in a single day, while in Hawaii there are zero casualties after weeks of spectacular lava flow. What’s the difference? Keith Bell, a geochemist and professor emeritus from Carleton University, has a simple explanation for it.
Hawaiian volcanoes are considered “some of the friendliest on earth.” They are “shield” volcanoes that are wide and shallow, like a warrior’s shield, full of fluid, lowviscosity lava. Kilauea, on the Big Island, remains in the news but has actually been flowing since 1983 and is generally so tame there is a parking lot next to its crater.
And El Fuego? Spanish for fire, El Fuego comes from the school of “nasty ” volcanoes, Bell says, socalled strata volcanoes chock-full of thick, high-viscosity lava that results in catastrophic eruptions.
“The magma is so sticky, that it can coalesce in the throat of the volcano,” Bell says. “Once it does that, gases start to build up, you get pressure exceeding the pressure above and you get an explosive eruption.
“That’s the main difference between a friendly volcano and an unfriendly one, it’s a function of the chemical composition of the magma and how viscous it is,” Bell says.
HIGH VISCOUS EQUALS VICIOUS
High viscous magma is thick like honey versus water, which has low viscosity.
“Here’s the point,” Bell says. “Hawaii has been erupting since May 3. How many have died? There have been no serious injuries as far as I know.
“Sunday, this damn thing went off in Guatemala and 60 people were killed just like that. It all depends on the makeup of the magma.
“It’s the worst type of eruption. The one that wiped out Pompeii (in 79 AD).”
According to Bell, the iconic volcanoes in history — think Vesuvius and Krakatoa — are strata in nature, like El Fuego. Hot, broken rocks called pyroclastic material combined with gas are thrown tens of kilometres into the air.
“What goes up, must come down,” Bell says. “Gravity takes over and you’ve got this mixture of gas and hot rock that just plummets down ... and the temperatures are 700 or 800 degrees travelling at 700 kilometres per hour.
“I was looking at some photos yesterday of El Fuego and people were trying to run away — you could see the flow overtaking them.”
Bell, who has studied volcanoes and the rocks they contain in such regions as Italy, Japan, Nicaragua, East Africa and the Russian arctic, says that strata volcanoes are so dangerous even expert volcanologists have been killed by pyroclastic flows while studying them.
VOLCANO FACTS:
Bell is one of few on earth to have flown by chopper over Kilauea, the current hot spot on the Big Island, which contains five volcanoes.
The earth’s core is more than 2,800 kilometres below its surface. “A volcano is a natural way to sample what’s down there,” says Bell.
Trade winds tend to blow these dangerous gases offshore, but when winds turn inward breathing can be difficult, even when the volcano is relatively quiet.
Volcanic smog (nicknamed vog ) is made of water vapour, carbon dioxide and highly toxic sulphur dioxide. There are also shards formed as the lava chills, like shards of glass. “Can you imagine breathing all this?” Bell says.
Mauna Loa, the western neighbour of Kilauea, is one of the largest structures on earth, and is the world’s largest active volcano. If you were to drain the water from the Pacific Ocean, the heights of Mauna Loa and nearby Mauna Kea would both be higher than Mt. Everest. Kea is about 4,200 metres above sea level and Loa is 4,170 metres. Though Kea is slightly taller, Loa is a much larger volcano.
There is a possibility that the current activity on Kilauea could trigger Loa to blow. “The plumbing system is very complex,” Bell says.
Lava flow from Kilauea is generally so predictable tourists can take pictures of it flowing to the sea, where it hits water and forms plumes of gas visible for several kilometres.
The volcanoes on the Big Island are younger than the volcanoes on the other islands, such as Kauai, Oahu, Molukai and Maui. The direction of the tectonic plates is moving toward the Big Island. Plumes form on top of the plates, get piggybacked, and when the plate movement pauses, volcanoes happen.
The Hawaiian islands are part of an immense submarine ridge that contains about 80 volcanoes, most of them under water.