Uncorking the secrets of a tiny bottle of volcanic ash

Uncorking the secrets of a tiny bottle of volcanic ash

I opened the living room window in our rented Anchorage waterfront condominium on what began as a mild mid-August day in 1992.

I don't remember what I was expecting when I looked across Cook Inlet that evening, but it wasn't my face being speckled with volcanic ash.

Mount Spurr, 78 miles west of our living room window, erupted at 4:42 p.m. Aug. 18. By 7:45 p.m., its ash cloud had spread nearly 200 miles southeast and reached almost 9 miles high, darkening Anchorage more than two hours before sunset.

The volcano erupted in June, August and September that year after 39 years of slumber, but the August eruption had the greatest impact. It dropped about one-eighth of an inch of ash on Anchorage. People wore masks and put pantyhose on their vehicle air intakes.

This week marks 34 years since my wife, Julie, and I scooped about an eighth of a cup of Mount Spurr ash and put it in a tiny clear, cork-stoppered glass jar. I can't remember if we scooped it off the hood of Julie's GMC Jimmy or somewhere else around the condo unit.

I know we didn't scrape it off the front stairs landing. That's where I wrote our names in ash. We were getting married in less than two weeks, you see.

Our little jar of ash has traveled with us through several moves in Anchorage and Fairbanks. It has sat on numerous shelves and in many nooks.

It's always been just "Mount Spurr ash."

But now that I work at the University of Alaska Fairbanks Geophysical Institute, which supports the Alaska Volcano Observatory along with state and federal agencies, I got to wondering:

What actually is that material inside our jar?

For answers, I took the jar and some of our old eruption photos to Nathan Graham at the Geophysical Institute's Advanced Instrumentation Lab. Graham, a volcanologist and the lab's director, had agreed to give the ash a basic examination.

"The cork is pretty old," Graham said, working it free with a latex-gloved hand. "OK, it looks like an ancient dog hair also made its way in there."

Well, that was unexpected. We didn't have any dogs back then.

Graham used a thin metal scoop to withdraw a tiny amount of ash grains.

"There's another little dog hair."

I wasn't the only one watching Graham work in the instrument's small room. His volcanology graduate student, Ian Carpenter, stood in the doorway. Undergrad Sarah Finney, who has studied Mount Spurr and Mount Redoubt, popped in and checked out my old photos, especially one showing an ash-blackened Anchorage sky.

"Whoa. That's the middle of the day?"

As she looked at the photos, Graham sprinkled some ash grains on a small adhesive disk, slightly smaller than a dime, and placed it inside the lab's scanning electron microscope.

"Usually what I would do if I were trying to get really nice images of this ash is I would clean it first," Graham said. "I'd put it in some water and give it a little sound bath to knock all of these tiny particles off the surface of it."

That wasn't needed for my ash. I just wanted a high-level look at what Julie and I had been toting around for three-plus decades.

Our well-traveled ash was now ready to be zapped.

"We generate our electron beam up here at the top of the instrument's column," Graham said. "A series of magnets and lenses in the column allow us to squish and manipulate that beam to be what we want it to be by the time it hits the surface of our sample."

A variety of sensors detect the electrons that bounce off the sample, with each sensor revealing different information about the sample's surface and structure.

The beam also causes the sample to give off X-rays as incoming electrons knock some of the sample's electrons out of their normal positions within atoms. The different energies of those X-rays can help identify the elements in the material.

With our vintage ash in a low vacuum and being pummeled by electrons, it was time for our first look.

An image appeared on Graham's computer screen. He zoomed in to a single grain at 800 times magnification. It looked to me like a microorganism, not a piece of lifeless volcanic ejecta.

Graham leaned closer to his screen.

"In the back you can see a kind of rippled surface," he said. "This is mostly a big

ger chunk of volcanic glass that has really fine ash particles stuck to the surface."

By "bigger," he means approximately 1 millimeter in length, about the size of a coarse grain of sand. Its attached particles measure about 1 to 5 micrometers, roughly the size of many bacteria. Even the largest are smaller than the roughly 7-micrometer diameter of a human red blood cell.

"And here are some vesicles. That's where gas was trapped inside the glass," Graham added.

I was hungry for more information, so Graham turned to the X-ray analysis. He selected a small area of another ash grain on the computer. The software produced an elemental spectrum with three sharp peaks.

Those peaks are like fingerprints. The position of each peak helps identify the elements in that part of the grain.

"This has a signature similar to a mineral called plagioclase," Graham announced. "It is mostly silica, aluminum and calcium, with a little sodium."

We wrapped up in the lab, and I headed back to my workspace. As sometimes happens, though, it wasn't long before I had another question. Could the ash tell me how and where it formed?

I checked with Pavel Izbekov, a research associate professor at the Geophysical Institute. He's been studying volcanoes for a long time and loves ash and the stories it can tell. He told me about collecting samples along the Parks Highway from the 2009 Mount Redoubt eruption.

Our ash grains, Izbekov said, were once part of a nearly solid mass of magma that had risen toward the surface and run out of places to move.

"They were connected to each other and suddenly got fragmented due to a pressure difference," Izbekov said.

As magma rises toward the surface, the pressure around it drops. Water and other gases dissolved in the magma form bubbles that expand. In nearly solid magma, those gases can become trapped.

Pressure builds as more gas comes out of solution and the bubbles continue to expand. If the pressure becomes too great, the magma can violently shatter and explode from the volcano.

"The majority of the material is fragmented to microscopic particles," Izbekov said. "This is precisely what fragmented your material."

Now we know a lot about the contents of our little glass jar. Except for those two dog hairs.

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided the Alaska Science Forum column free in cooperation with the UAF research community. Rod Boyce works in the Geophysical Institute public information office.