By Edwin Schiele
October 22, 1998. This research cruise differs from most others in that we are often in sight of land. On a clear day when we are working close to shore, I (and others) will take some time off, move to the bow away from the constant drone of the winch, and stare at the Big Island. The slopes on the island are gradual with few bumps or jagged edges. Yet the land is not featureless. Part way up the slope, clouds of steam billow up from a low but broad cone that has the classic look of a volcano. This is the Puu Oo crater. Just down slope, smaller puffs of steam rise from skylights in the lava tubes. In the far distance, it is possible to see steam generated from the lava entering the ocean.
Rain clouds often obscure the higher elevations, but when they part, they reveal the two most massive volcanoes in the world; Mauna Loa and Mauna Kea. You would have to go to Mars or Venus to find any that are bigger. Both rise over 13 thousand feet above sea level. They dont, however, look like classic volcanoes. There are no steep, symmetrical, flat-topped cones visible. From the ship, Mauna Loa appears golf-course smooth (although it would be a lousy place to play golf.) Its slopes are gradual to the point of barely being perceptible. The older Mauna Kea is lumpier, but its slopes are also gradual. On a clear day, it's possible to see the sun glinting off the white astronomical observatories on top.
Shield volcanoes, such as Kilauea, Mauna Loa, and Mauna Kea, typically form over hot spots. Yet not all hot spots produce volcanoes that look like these three. Travel 600 miles off the coast of Ecuador to the Galapagos Islands and you will find a different type of volcano altogether.
The Galapagos Islands are best known for their biodiversity. Like Hawaii, the isolation of the Galapagos has given rise to a group of plants and animals, including giant tortoises, swimming iguanas, and finches with different shaped beaks, that are found nowhere else in the world. People often dont realize, however, that like Hawaii, the Galapagos Islands are constructed from a series of hot spot volcanoes. There are 11 historically active volcanoes on the Galapagos Islands (Hawaii has four), although they are far smaller than the Hawaiian volcanoes. (The tallest is 5,400 feet). One of them is erupting right now. Whereas scientists know more about the Hawaiian volcanoes than they do about any other volcanoes in the world, they know practically nothing about the Galapagos volcanoes.
Denny Geist and Terry Naumann are two of the first scientists to take on these volcanoes. After hearing about the conditions in which they must work, I more fully appreciate the climate-controlled luxury-liner we live on where they feed us three times a day and provide us with all the water we could hope for. Typically a boat deposits Denny, Terry, a porter/guide, an Ecuadorian student, and a months supply of canned tuna, rice, and water on an isolated piece of coast. The Galapagos Islands are mostly desert, so the temperatures can be brutal. They then must haul their supplies up hot, dry, steep, aa-covered slopes to their study sites. (I havent had the pleasure of walking on aa flows, but I am told the jagged lava destroys boots as well as the skin of those who fall on it). All they are missing are maps. That is because maps of the volcanoes do not exist.
Their field work is basiccollect rock samples and try to compare the ages of different lava flows. Without topographic maps, they can do little else. They have, however, found some surprising differences between these volcanoes and the ones on Hawaii. The Hawaiian volcanoes erupt along well-defined rift zones. For example, the current eruption on Kilauea, as well as all the eruptions that formed the Puna Ridge, occurred along the East Rift Zone. The Galapagos volcanoes do not have rift zones. Instead, lava erupts all around the flanks. The results are volcanoes that are shaped like upside-down funnels, not shields. The slopes grow steeper towards the top. These volcanoes also have enormous calderas that extend from the tops of the volcanoes half way down to sea level. Denny and Terry must often climb down these calderas to collect rock samples.
So why do these volcanoes differ from those on Hawaii? Denny and Terry speculate that part of the answer may be the position of the hot spots. The Hawaiian volcanoes sit in the middle of the Pacific plate where the lithosphere is old and thick. The Galapagos volcanoes sits next to a midoceanic ridge, so the lithosphere is much younger and thinner. By analyzing the composition of the magma, Denny, Terry, and others hope to learn how the locations of the Galapagos volcanoes influence the types of eruptions.
The study of the Galapagos volcanoes will soon move into a new phase. Denny has a grant to use GPS (global positioning satellite) to create the first topographic map of the Galapagos volcanoes. The GPS will also enable him to detect changes in the volcanoes such as swelling or movement. Although this information will go a long way towards helping scientists understand the dynamics of these volcanoes, it wont help them carry those cans of tuna from the bottom to the top.