The following is an excerpt from the book Surviving Galeras by Stanley Williams.
Chat with Stanley Williams beginning at 4 p.m. (EST) Friday. Also, buy your copy now.
My colleagues came and went in the clouds. Banks of cumulus drifted across the peaks of the Andes, enveloping us in a cool fog that made it impossible to see anything but the gray rubble on which we stood. Perched at 14,000 feet on a cone of volcanic debris in southwestern Colombia, we were checking the vital signs of Galeras — gases, gravity, anything that would tell us whether the volcano might erupt.
As morning gave way to afternoon, the clouds occasionally dispersed, offering a heartening glimpse of blue sky and revealing Galeras's barren, imposing landscape. At the center of the tableau was the cone, 450 feet high, and its steaming crater. Surrounding the cone on three sides were high walls of volcanic rock, known as andesite. Forming an amphitheater 1.3 miles wide and open to the west, these ramparts were a subtle palette of dun, battleship gray, and beige. The top of the escarpment was composed of crumbling columns of hardened lava, the bottom a steep incline of rock and scree. All of it was the remnant of an earlier volcano that had collapsed thousands of years ago, spilling its contents down the mountain in a vast debris field. Occasionally I glimpsed in the west a forested, razorback ridge sloping toward the equatorial lowlands 9,000 feet below. That was the flank of an ancient volcano, which imploded 580,000 years ago after a massive eruption.
For miles around, the landscape was defined by these vestiges of earlier Galerases in various stages of decay and erosion.
Around one in the afternoon, I stood with four other geologists on the crater's lip and gazed into the steaming pit. Like the craters of most explosive volcanoes, this was not a cauldron of lava. It was a moonscape. Some 900 feet wide and 200 feet deep, the mouth of Galeras was a misshapen hole strewn with jagged boulders. Much of that rubble came from a hardened magma cap, or dome, that had been blown to pieces six months earlier in an eruption. At first glance, the crater seemed a sterile place, its colors running a dreary spectrum from dark gray to brown to beige. But on closer inspection the mouth revealed pockets of color — rust-hued swaths of rock breaking down in the heat and gases of the crater and canary-yellow patches of sulfur that had accumulated next to a gas vent, known as a fumarole. These vents were small fissures where high-pressure gases were released from the magma body beneath the volcano. The gases, which assaulted the nostrils with a melange of sharp, acrid odors right out of the chemistry lab, shot from the fumaroles with a hiss, obscuring the landscape in a swirl of vapors.
Galeras's fumaroles were relatively quiet that day, emitting a whooshing sound much like that of a steam machine used to clean buildings. When you step down into such a crater, the howl of the wind at 14,000 or 16,000 feet is instantly replaced by the eerie quiet of the earth's interior. The exception is when volcanoes are riven by high-pressure, high-temperature fumaroles. Then you feel as if you are planted behind a jet engine as it prepares for takeoff. Such fumaroles are not encircled by yellow sulfur crystals, which form at lower temperatures, but rather by a bathtub ring of expelled minerals in black, orange, blue, and white.