One of the more amazing impacts of the 7.1 magnitude earthquake that rattled Southcentral Alaska on Nov. 30 went largely—and perhaps entirely—unnoticed by Anchorage-area residents until days later.
The same hard shaking that damaged local buildings and roads and showered sections of the Seward Highway with rock debris also unleashed a major landslide and rock fall from the southwestern flanks of Rainbow Peak, thousands of feet above Turnagain Arm and the trail that bears its name.
It doesn’t appear that any of the boulders released in that massive rock slide reached the Seward Highway far below, but some of the larger ones might have careened down to the road if not for a stony, forested knob that juts above Beluga Point. (All the rocks that fell on the highway seem to have come from the cliffs that immediately rise above it, not from higher on the mountain.)
A sign posted at the Turnagain Arm Trail’s Rainbow Trailhead warns hikers, “Since 11/30/18 earthquake a major landslide and continuing rockfall have been noted from Rainbow Peak. Use trail at your own risk. Be prepared to turn back.” But in response to questions I sent his way this spring, Chugach State Park trail specialist Joe Hall informed me that “All of the damage [to the trail] did occur during the main earthquake. We heard about it from trail users within a couple days” of the quake. “We’ve been monitoring it since, and no additional damage or slides have occurred.”
Park superintendent Kurt Hensel confirmed Hall’s observations in early June and added that the trailhead warning would soon be removed.
In his comments to me, Hall further noted that he and a volunteer walked the trail’s McHugh-Rainbow section within a week or so after the slide to clear broken and downed trees from it and do some repairs on the “damaged tread.” Even then the entire route remained navigable, though hikers had to work their way around some of the larger boulders that came to rest right on the trail.
I first noticed the slide in early April, during my first springtime hike along the Turnagain Arm Trail (TAT) this year. As I noted in an earlier “City Wilds” column (Early Spring Delights Brighten the Turnagain Arm Trail, https://www.anchoragepress.com/sports_and_outdoors/early-spring-delights-brighten-the-turnagain-arm-trail/article_9e9de3c6-6b9f-11e9-9a2c-4b80fe3fc23f.html), the McHugh-Rainbow section is the best place to find the earliest signs of local woodlands’ annual rebirth, especially in the form of sprouting plants, the opening of leaf buds, the blossoming of wildflowers, and the songs of returning migratory songbirds.
Evidence of the Nov. 30 rock slide is indeed impressive, as anyone who has recently walked that stretch of trail can testify. Large boulders are randomly scattered along more than a mile of the trail (between mileposts 4 and 6), in the company of trees that were smashed and snapped by the careening rocks.
It’s hard to tell if all of the boulders came from the same location high above or whether there were multiple “release points.” I haven’t tried climbing through the forest to find exactly where the rock slide(s) began and I’d be curious to know if any readers of this column have done so, and what they’ve found. I wonder too if the place where the rocks exploded off the mountain can be seen from the path that leads from the Turnagain Arm Trail up to the summit of Rainbow Peak. That could be something worth checking out.
Though boulders from the November 30 rock slide occur sporadically along a substantial section of trail, the greatest concentration of them—and the most compelling evidence of the damage those boulders did to the forested landscape—occurs a short distance beyond Milepost 5.
Looking uphill, one can see the paths taken by the largest and most destructive boulders, marked by several rows of snapped and fallen trees, many (and perhaps most) of them impressively large, mature cottonwoods. Immediately above, across, and below the trail the boulders have gouged large trenches; and alongside the trail are dozens of mangled and broken trees. Again, most are cottonwoods but spruces and birches have also been clobbered.
Several of the boulders continued on their lurching paths below the trail and it appears the larger ones might have tumbled much farther—perhaps even to the highway—except for that rocky knob I mentioned earlier, which stopped their downhill charge. The largest boulder that I saw was the size of an RV; it dwarfed my mixed collie when Denali climbed upon it.
How long did the rock slide last, I wonder. A matter of minutes? Or did boulders continue to bound downhill for many hours after the earthquake, some set loose by aftershocks?
It would have been terrifying to be on the trail (or in those woods) when the mountainside let loose. There must have been a huge explosion, followed by a deadly torrent of falling rocks, making their own sort of frightening, thunderous crashing.
When Jan Myers joined me on a hike to see the rock fall’s aftermath, we tried to imagine what our response to the slide would have been. Even the strategy of seeking cover might have been futile if you were in the slide’s path, unless you could find a large enough rock wall to duck behind.
The broken trees and gouged trenches make it clear that the boulders were bounding across the hillside, sometimes in a helter-skelter way that would make it all but impossible to guess where they might land or leap next. Many trees were broken high above the ground; the trunk of one cottonwood had been snapped 20 to 30 feet above its base. And even the largest of trees had been smashed to fragments or knocked to the ground, if hit directly.
The slide would have been awesome to observe, if seen and heard from some safe distance; and awful to behold, if in the rock fall’s path.
Anchorage nature writer Bill Sherwonit is a widely published essayist and the author of more than a dozen books, including “Living with Wildness: An Alaskan Odyssey” and “Animal Stories: Encounters with Alaska’s Wildlife.” Readers wishing to send comments or questions directly to Bill may do so at email@example.com.