Mount Hood's crater is rimmed with unstable cliffs, which can collapse and send an avalanche of rock down the mountain. Timberline Lodge is located on the remnants of one such event. (Photo: Adam Kent)

Mount Hood last erupted more than 200 years ago, but at Crater Rock, not far from the summit, the signs of volcanic activity are unmistakable. Gas vents and hot springs emit sulfur fumes. Vapors rising from deep under the mountain carve snow caves, which can seem like sanctuaries for climbers but often hold deadly concentrations of CO2 and other gases. Rocks fall frequently from the steep unstable cliffs of the partially collapsed crater.

Odds are low that Oregon’s tallest mountain will erupt any time soon, but when it does, scientists have a pretty good idea of what will happen. Driven by the grinding of tectonic plates deep in the planet’s crust, hot magma will infuse cooler lava chambers closer to the surface (an event geologists call “recharge”). Pressure will build. Rocks will begin to crack.

In some volcanoes, not much happens after recharge. The lava chambers may be hotter and ready to burst, but the lid stays on, and the molten rock gradually cools. It takes quite a punch to force a mass the consistency of oatmeal up through miles of tortuous fractures.

Hood, however, is impatient. Within weeks of recharge, lava starts moving and gases start bubbling out through the crater. Melting snow and ice generate debris flows down the mountain’s flanks sweeping away forests and filling rivers with sand and rock. (In the distant past, such events have careened down the Hood River valley and across the Columbia River.) Eventually, lava emerges and snakes down the mountainsides, adding to Hood’s bulk and remaking its classic profile.

That’s been the story for more than a half-million years, says Adam Kent, Oregon State University geologist. When he first arrived in Oregon in 2003, the Australia native learned that while scientists from the U.S. Geological Survey’s Cascade Volcano Observatory knew a lot about hazards posed by eruptions, Hood’s underground plumbing remained largely a mystery.

Since then, Kent has analyzed the remnants of old lava flows to learn how the mountain behaves. He and post-doctoral researcher Alison Koleszar have climbed to the crater, brought samples back to their labs and squeezed clues from rocks. The chemical composition of Hood’s lava flows has remained amazingly uniform over the centuries, and they have found that the mountain may represent an extreme end of volcanic systems and may in fact be unique in the Cascades. Unlike Mount St. Helens, Mount Jefferson and others in this spectacular range, Hood doesn’t explode; it oozes.

Crystal Visions

Kent keeps a piece of Mount Hood in his office. This flat gray rock looks like some kind of exotic concrete. It sparkles with crystals. Irregular, coffee-colored spots about the size of a quarter dot its surface. Dark flecks of hornblende (composed of iron, calcium, silicon and magnesium) are scattered across its surface like pepper on a fried egg.

“When this rock came to the surface,” Kent says, “it was partly liquid. It records information about the last stage of the eruption. But if you want to know more about the long-term conditions in the crust where this magma was being stored, you need to look at the crystals.”

Like tree rings, crystals grow from the inside out over time, says Kent. At their heart are the original minerals — formed out of common elements such as calcium, iron, silicon, magnesium and aluminum. As hot rock pulses up from below, crystals go through warming and cooling phases. Mineral layers form on the outside edges and create a record of temperature, pressure and chemistry. Each ring tells a story about a new pulse of melted rock that cycled the crystal through heating and cooling.

This false color image of a feldspar crystal embedded in a rock from Mount Hood shows the rings generated by pulses of magma from deep in the crust. The outer edge was created during the event that caused the mountain to erupt. (Photo: Adam Kent)

Crystals also trap tiny remnants of some of the original parent material, melted rock that is created as tectonic plates grind against each other. Analysis of these trapped particles — what geologists call “melt inclusions” — provides a picture of the minerals and volatile gases (water, carbon dioxide, sulfur, chlorine and fluorine) that emerge from deep in the crust and can give a mountain shape and personality. When concentrations of those gases are high, explosive eruptions are more likely.

To find out what distinguishes Hood from its neighbors, Kent, Koleszar and their team separate crystals from surrounding rock. In the Oregon State geology lab, they subject samples of the mountain to diamond-tipped saws, acids and devices that pound stones into dust or polish them to a fine sheen (Polishing can be pricey. Grinding pastes that contain diamond particles can cost upwards of $300 for half an ounce). They separate crystals further by exposing rock fragments to magnetic fields or dropping them in dense liquids.

“Some samples are crumbly and fall apart easily,” says Koleszar. “Those are harder to work with. Nice clean pure volcanic glass is great. It polishes like butter. It’s so soft compared to some of the minerals we use.”

Once separated, sliced and mounted on slides, crystals undergo analysis by electron beam that reveals fine structural details or laser and mass spectrometry that tell scientists what trace elements are present in each crystal ring. The result is an accumulation of evidence that allows geologists to explain Hood’s eruption process and compare the mountain to other volcanoes.

More Fizz, No Pop

In a paper published in the Journal of Volcanology and Geothermal Research in 2012, Koleszar and co-authors Kent, William Scott of the USGS and Paul Wallace of the University of Oregon described their findings. They reported that Hood’s magma contains the ingredients for explosive eruptions: magma pumped regularly into the mountain from below, a chemical profile similar to that of other explosive volcanoes and high levels of volatile gases. However, at Hood, those gases tend to escape readily like fizz from an open can of soda. That’s because a 100 degree increase in temperature — an increase that happens as hot rock flows into magma chambers under the mountain — makes the flowing rock five to 10 times less thick.

“Imagine you are blowing into a straw in a milkshake,” says Koleszar. “It’s so thick that the bubbles don’t come out right away, but when they do, they burst and throw stuff up in the air. Compare that to blowing into a straw in a glass of milk. Bubbles just come easily to the surface. That’s more like what we see at Mount Hood.”

Alison Koleszar, left, and Tyler Lomax, a junior from Albany, Oregon, collected rock samples from the 590,000-year-old Cloud Cap lava flow on the eastern side of Mount Hood. Composition of the rocks there is thought to reflect the original parent magma. Koleszar and Lomax also trekked through lava fields on the southern flank where flows are less than 30,000 years old. (Photo: Jeff Basinger)

Mount Hood may be unique in the Cascades, but it joins a select group of volcanoes worldwide (Mount Unzen in Japan, Soufriére Hills Volcano in Montserrat, Mount Dutton in Alaska) that tend to ooze instead of explode. Nevertheless, volcanoes can also demonstrate both types of behavior, and there’s no guarantee that Hood will always operate as it has in the past. Two well-known explosive volcanoes — Mount Pelée in the Caribbean and Mount Pinatubo in the Philippines — have exhibited both types of eruptions. Moreover, geologists know that pulses of hot magma, which occur at Mount Hood, can cause explosions such as the 1980 Mount St. Helens eruption.

“We’re still trying to figure out why Hood only erupts right after a recharge event,” says Koleszar. “It may be that it just doesn’t have the oomph to erupt at other times.

“It seems like such a boring volcano,” she adds. “It erupts the same thing all the time; it doesn’t seem to do anything interesting. It’s an icon, it’s a beautiful volcano and it’s Oregon’s volcano. But when you start to tease things apart a little bit, it does get interesting, exactly because it is so boring.”

_____________________________

Download an animation of magma rising into a volcanic crater. Scientists can sample the resulting airborne plume to understand how the volcano is likely to erupt. (Produced by the Johnston Ridge Observatory at Mount St. Helens in collaboration with the U.S. Geological Survey)

WeiLi Hong (Photo: Lee Sherman)

When the Earth burps, WeiLi Hong listens. Whether Earth’s gaseous emissions bubble up from “mud volcanoes” on the planet’s surface or seep out of fissures on the ocean floor, the Oregon State University Ph.D. student has his monitoring gear to the ground.

And sometimes, he’s actually in the ground.

“I fell in twice,” Hong admits, describing the hazards of surveying mud volcanoes in his home country of Taiwan. “I was trapped in thick mud up to my waist. There was nothing solid to grab onto. I had to kind of roll across the surface of the mud until I could pull myself out.”

Which brings up a couple of questions: What is a mud volcano, anyway? And why would anyone risk life and limb traipsing around these oddities of nature?

The answer is methane — millions and millions of tons of it trapped in ancient sediments. Under pressure from the bumping and grinding of tectonic plates, the gas migrates upward through Earth’s crust, seeking the atmosphere. Certain countries, such as Taiwan, Indonesia, Pakistan and Azerbaijan, are “burping gas like overfed infants,” to borrow a metaphor from one New York Times writer on the subject of methane emissions. As the methane escapes, creating a slurry of fluids and dissolved solids, volcano-like mud domes mound up across the landscape. They can be as small as a toddler’s backyard swimming pool and as big as several kilometers in diameter.

Mud can act like quicksand. WeiLi Hong needed a helping hand during his research in southern Taiwan. (Photo courtesy of WeiLi Hong)

WeiLi Hong conducts mud volcano science in Taiwan. (Photo courtesy of WeiLi Hong)

But that’s not the only way methane migrates. It comes up through the bottom of the ocean, too. On the seafloor, where it’s super-cold, seeping methane gets locked into ice-like structures called “hydrates,” Hong explains. Studying methane emissions on land, despite the pitfalls, is a walk in the park compared to studying them 2,000 feet beneath the sea.

“With mud volcanoes, we’re looking at how much methane is emitted to the atmosphere,” says Hong, who specializes in chemical oceanography in the College of Earth, Ocean, and Atmospheric Sciences. “With cold seeps, we’re looking at how much methane is emitted to the water column. To do that, we need a vessel with the ability to drill.”

The discomforts of being at sea for two months didn’t deter Hong two summers ago when, along with OSU researcher Marta Torres, he joined an exploratory expedition to Korea’s East Sea hunting for hydrates aboard the research ship Fugro Synergy. His job was to analyze the physical properties of sediment samples taken from the depths.

Methane hydrate will burn when lit. The inset image shows the structure of methane hydrate; the green and grey molecule in the center is methane and the red cage is the ice structure. (Photo courtesy of the National Oceanic and Atmospheric Administration)

For scientists and engineers, this trapped methane presents both threats and opportunities. On one hand, Hong says, melting hydrates could trigger Earth-warming greenhouse-gas emissions and tsunami-causing landslides. On the other hand, methane could be an energy bonanza — if it could be safely harnessed. That’s why the Korean government and the U.S. Department of Energy cosponsored the 2010 Ulleung Basin Gas Hydrate expedition.

“We were looking at porosity, permeability, texture, composition,” he says. “We used an X-ray machine to get 3-D images of the cores.” Opening his laptop, he clicks on a grainy gray image from the bathysphere. As he toggles the image this way and that, he points out traces of long-dead organisms in the long-buried layers. “On the computer,” he notes, “you can rotate the sediment column to see how the geosphere, hydrosphere and biosphere interact.”

_____________________

For more information about education abroad opportunities for OSU students, contact the International Degree & Education Abroad (IDEA) office at 541-737-3006.

(Illustration: Santiago Uceda)

An erupting undersea volcano near Guam in the western Pacific continues to reshape the seafloor. In March 2010, scientists from the National Oceanic and Atmospheric Administration and OSU led another in a series of expeditions to NW Rota-1 in the Mariana Arc. Eruptions have been practically continuous since first discovered in 2003, says Bill Chadwick, chief scientist for the project.

In August 2009, intense volcanic activity culminated in a dramatic landslide that extended up to five miles from the top of the mountain. Instruments deployed to monitor volcano activity were destroyed by the avalanche. A hydrophone survived intact and recorded the event, which lasted for five to six hours. The volume of material that slid off the mountain would have filled about 250,000 railroad boxcars, says Chadwick.

Chadwick presented expedition results at the annual meeting of the American Geophysical Union in December  2010.

___________________________

For information about supporting research and teaching through faculty endowments, contact the Oregon State University Foundation, 1-800-354-7281 or visit CampaignforOSU.org.