So Many Mountain Ranges, So Little Time

Just South of Haggard Creek, Pipeline Mile 643--Please humor me and read this column, because I worked hard for the setting in which I wrote it.

In this space, I'll compare the Alaska mountain ranges I'll walk through this summer--the Chugach, Alaska, and Brooks. To acquire the proper writing mood, I chose an elusive overlook just off the pipeline. From here, I can simultaneously see the Alaska Range, the Wrangell Mountains, and the Chugach Range. To spend some time here, I've toted my water from a creek a half-mile of hilly, crumbling rock away, and I'm ignoring my fear of scat piles so large I'm wondering if they filmed the Jurassic Park sequel here.

If you need another reason to scan further, know that Erin Parcher, an amazing student assistant at the Geophysical Institute, helped me gather the notes for this column. Erin's leaving soon to share her ample brain as a teacher. She may be gone by the time this column hits the paper. Our loss.

Back to the mountains. The Chugach Range appears to the south of my eagle's nest as distant white pyramids. Geologists think the Chugach Range probably did quite a bit of traveling to sit where it does today, in a 250-mile swath across Alaska from Anchorage to Valdez and points east.

How do mountains move? The rocks that make up the Chugach Range caught a ride on the Pacific plate, a mammoth portion of Earth's crust that dives under the North American plate in Alaska. Earth's crust is made up of about a dozen plates--gigantic slabs of rock that are more than 1,000 miles across and up to 40 miles thick.

Over millions of years, the rocks of the Chugach Range made a long journey from the south, and the adjacent Wrangell Mountains came from as far away as the tropical belt just north of the equator to settle in Alaska.

For some odd reason, the rocks that were to be the Chugach Range didn't dive beneath the North American plate. The collisions of the Chugach fragments with what is now Southcentral Alaska resulted in the gradual uplift of the Chugach Range. Today, the older Chugach rocks are found further inland, while the relative youngster rocks hang along the coast.

As I look north, I see the next obstacle in Jane's and my path--the Alaska Range. The home of Mt. McKinley curves from Canada all the way to the Alaska Peninsula. Like the Chugach Range, the Alaska Range consists of rocks that originated elsewhere on the planet, but the Alaska Range differs in that it has a core of granite.

The granite hearts of mounts Hunter, Foraker and McKinley were all formed rather recently in geologic time, about 60 to 40 million years ago.

Why is Mt. McKinley, at 20,320 feet, so tall? It depends on which geologist you ask. Some say it's because Mt. McKinley formed at a bend in a fault system--a weak point in Earth's surface where one piece of crust shoves against another. All that pushing at the bend may have resulted in Earth's overachievement. Another theory is that a lighter block of Earth's crust was dragged under Alaska by a force called subduction and is now pushing up from below (and getting its picture taken thousands of times a summer).

Though I have a great perch here, I can't see the last group of mountains I'll cross on this trip--the Brooks Range. The Brooks Range, my personal favorite and a major impetus of this trip, extends for 600 miles in an east-to-west band above the Arctic Circle. The following is based on my interview last summer with Gil Mull, a geologist with the Alaska Division of Geological and Geophysical Surveys.

Brooks Range peaks are often whitish and tend to tilt at dramatic angles. The white is limestone; in the Brooks Range limestone tells a story of the area's past.

About 400 million years ago, much of the area of the Brooks Range was a waist-deep sea. Limestone is often composed of the remains of shelled sea creatures. After the calcium-rich creatures died, their shells broke down into limestone mud, which eventually hardened to stone.

About 145 million years ago, an earlier Pacific plate began acting as a snowplow, shoving itself over the top of the North American plate and stacking layers of limestone, sandstone and other rocks to form the incredible Brooks Range.

Sometimes on this trip I can't wait to be in the Brooks Range. With a view like I have now, though, the Brooks can wait.