by J. Besl |
This is the first in a three-week series covering Anchorage Field Studies, a UAA geology class taught by Dr. Kristine Crossen. The course spans the first five weekends of each fall semester, starting with a brief classroom component before students head off to explore geologic sites across the Anchorage Bowl.
The classroom for Anchorage Field Studies is an odd sight. For one, unlike college classrooms across the country, students fill the front row and leave the back completely deserted. For another, everyone is energized even though the class convenes at 9 a.m.-an hour many students avoid at all costs. Everyone made it to campus, despite the September rain pummeling the parking lot, and, oh yeah, the class meets on weekends. These kids truly love rocks.
But they also love their professor, Dr. Kristine Crossen, who has taught generations of UAA geologists over the last 30 years. "I couldn't imagine the department without Kris," geology senior Alex Busk added. "She's so knowledgeable. Her passion for geology is just amazing."
Kris's specialty within the department is Alaska geology and the processes that built the Great Land, making her the perfect professor to take students across the state. An obvious benefit of Anchorage Field Studies is the hands-on experience, but it's enhanced by Kris's encyclopedic knowledge. "This class is good to take if you're a visual learner. A lot of what she talks about you can't even search for," explained student Yosty Storms.
Many of Kris's students grew up in the Anchorage area, and the class is showing them a side of their city they may never have noticed. In addition, they're learning about the processes that shaped this postcard-perfect patch of land long before Anchorage's founders planted their tents on the sides of Ship Creek.
Recently, the class headed to Bird Point, a familiar stopover just 30 miles from campus down Turnagain Arm. But the rest area provides far more than just incredible vistas of the inlet. For geology students, it features evidence of the past 11,000 years of planetary history.
Down in the muck
Back during the Ice Age, up to 20,000 years ago, the area we call Anchorage was buried under a vertical mile of ice. Things have warmed a bit, but the remnants of that massive glacier are still visible, and so is the glacier's path of retreat. For example, the Anchorage Bowl is pinched by the claws of Turnagain Arm and Knik Arm, which terminate at Portage Glacier and Knik Glacier, respectively. These glaciers-and the giant waterways that lead to them-are leftover legacies of the mile-thick ice sheet that dominated the landscape. Anchorage residents are blessed to have the Seward Highway a mere 20 minutes away, but they have the retreating Ice Age glaciers to thank for the steep slopes that flank the Arm.
But it's one thing to talk in class about glaciers carving this valley and it's another to hike to the waterline. After parking their two big blue UAA vans at the Bird Point parking lot, Kris led her students down a hidden trail to a rocky outcrop on the water's edge. To the untrained eye, this was nothing special, but to a geologist this patch of rock was a rare sight. Bedrock at the water's edge is exceptionally rare along Turnagain Arm. Most of the local coastline-including in downtown Anchorage-is built of dangerous quicksand-caliber muck.
Anchorage may lack white sandy beaches but, then again, the frigid murky water isn't too inviting either. The steely gray sea is filled with muddy silt, earning Turnagain Arm a rare and uncelebrated distinction as one of the dirtiest fjords in the world. Extend those steep mountain peaks into the water and imagine how deep they must run before their slopes intersect beneath the water. Then fill all that in with grimy mucky silt. Turnagain Arm, it turns out, is filled with 1,000 feet of mud. "It's a very unusual situation as far as the world goes," Kris commented.
The birth of Sleeping Lady
So the patch of coastal bedrock is, indeed, a rare sight for geology students. As a lone bald eagle glided from a nearby tree and curious seals poked their heads out of an eddy, Kris posed the assignment to her students: identify concrete evidence of the direction of the glacier's trajectory.
A quick scan showed striations perpendicular to the rock's natural layering. Loose rocks picked up by the glacier once scraped along the bedrock, leaving a mark on the rock and indicating the two directions the glacier could have traveled. But the real answer lies in the roche moutonnée.
French for "sheep rock," roche moutonnée were first described in the French Alps, hence their interesting name. Essentially, it's an asymmetrical glacial-carved rock formation, typically featuring a slow sloping face on one side and a jagged craggy composition on the opposite. For an indicator of the massive scale of the Ice Age glacier that blanketed Anchorage, look no further than across the water- the asymmetrical Mt. Susitna is one giant roche moutonnée carved by ice descending from Denali through the Susitna Valley.
Geology student Phil De Land described more: "A rock naturally has creases and cracks, which are called joints," he said. "Basically, they're weaknesses in the rock that are inherent when the rock is formed." When a glacier scrapes along these weaknesses, the rock starts to separate along the joints. "The blocks are eventually going to topple over and get scooped out," Phil said.
Kris explained as much while seated in a giant hole in the bedrock. "It was like a bathtub, it was that deep," Phil recalled. That sizable divot was caused by plucking, a glacial process that pries out chunks of rock along the joints and drags them further downstream. This plucking accounts for an abrupt and often jagged appearance on the downstream side of the roche moutonnée.
With that in mind, the students could definitively indicate the direction of the glaciers original advance. The Alaska Railroad rattled past and the bore tide swept in while students recorded their final notes perched on the patch of bedrock. Tightening jackets against the rain, everyone headed back to the vans, though a lucky few stragglers were treated to a breaching beluga out in the water-just another epic addition to a wild day in Alaska.
'You couldn't ask for a better place to study geology'
According to Kris, Anchorage is home to the fourth-strongest geology industry in the country. Aside from exploring beautiful pockets of the city, her field studies course prepares students for a long, successful career in the North.
"Anchorage is one of the most interesting places I could be studying geology," noted Phil, a fourth-generation Alaskan. "You couldn't ask for a better place to study geology."
"We're actually in an exposed subduction zone. Other places in the world, they know it's there but they have to use geotech to find it. We can just walk out and look at it," he continued, gesturing to the Chugach Mountains. "It's right on the surface. It's perfect.
And you couldn't ask for a better course to experience it. Kris's students fill pages of their rain-stained notebooks on each weekend adventure. But they'll remember the class material long after the semester.
"We get so much information in the geology program," Phil added. "If you can be hands-on, that's a memory you can go back to 30 years later and remember exactly how things worked because you saw it."
"In my lifetime, we'll never run out of things to look at here in Alaska."
Written by J. Besl, UAA Office of University Advancement