It Hasta be Shasta

My most recent post (A Show of Hands) certainly woke up some of the usual suspects, and although it was not my intention to spark such impassioned rebuttal, it is comforting to realize that there are some who actually take the earth and its processes seriously. Thank you!

While the science of earthquake prediction may remain frustratingly out of reach, we DO know how to predict a looming volcanic eruption. Maybe not down to the minute, but close enough to get ourselves, and any portable infrastructure, out of the way — assuming the warnings are recognized and acted upon.

Before we jump in, please feel free to refer to the following for a bit of background (and follow the links as needed):

• Click here for an index to blog posts related to volcanoes.

• Click here for an Introduction to Volcanism.

• Click here for a discussion of mafic vs. felsic igneous compositions.

• Click here for an index to blog posts related to earthquakes.

• Click here for a discussion of tectonics along the west coast of the United States.

Anyway, we may be over-matched when it comes to predicting temblors, but how’s this for an all-too-realistic scenario with regard to volcanoes?

We learned all about harmonic tremors from the lead-up to the eruption of Mt. St. Helens in 1980. It’s safe to say that at the time we may have not have fully understood the reality of what they foreshadowed, but we sure do give them more respect now! Click here for an earlier post on these swarms of mini-quakes that are a somewhat accurate — although not foolproof — predictor.

So…. What’s gonna happen when Mt. Shasta, for example, starts to show the recognizable signs of an imminent eruption?

To put this into some regional perspective, Mt. Shasta is one of the active volcanic peaks of the Cascade Range in the Pacific Northwest. In case you were wondering: Yes, the Cascades are considered active by anyone who thinks in earthtime, and will remain active as long as spreading along the Mid-Atlantic Ridge continues to shove the North American Plate westward, where it collides with the plates that comprise the oceanic crust beneath the Pacific Ocean; in this case along the Cascadia Subduction Zone.

So here comes Shasta — stretching like a tomcat after a brief nap, and quivering with harmonic tremors, with maybe even some preliminary venting of steam and ash to clear the pipes in anticipation of the main event. How should we react?

Well, the initial step would seem to be clear. Like at Mt. St. Helens, the Powers That Be will need to set up and evacuate a “Red Zone” in the hopes of minimizing the local and regional casualties, and other effects. This would of a necessity involve moving out the residents and limiting access.

(Fun Fact about a Red Zone: A couple weeks after the main eruption at St. Helens, my partner and I were sitting at a construction stop along Hwy. 197 in eastern Oregon and happened to see ash from several smaller eruptions expand across the northern horizon. The next day we drove up the Toutle, around the Red Zone barricade, and got as far as we could before being stopped by a washed-out bridge. Dave was shagging golf balls towards the remains of the mountain while I was watching rocks float down the river, when the dudes with the flashing lights on their truck arrived. As a registered geologist, I managed to sweet-talk us out of the $10,000 fine with which they threatened us — assuming we could beat them back to the road block — but it was a near thing.)

At St. Helens, it became pretty obvious (see the image of the Northern Bulge, above) that it was going to be a flank eruption, as opposed to a summit blast like the one that turned Mt. Mazama into Crater Lake. But there are no guarantees that Shasta will offer us such an obvious indicator of direction. If that remains the case throughout the early rounds, the Powers will need to be proactive everywhere… especially downstream.

So, what’s downstream? Well, the headwaters of the Sacramento River are up by Mt. Shasta, and the drainage extends down past Sacramento to the Delta and from there dumps into the San Francisco Bay. Following the course of the river are two major transportation arteries: Interstate-5, and the main north-south railway.

Once Shasta begins showing signs of an eruption, the guys in charge are going to have to close both the railroad and I-5, each of which is critical for the movement of people, goods, and services along the west coast. Let’s ignore the railroad for now (although its disruption may be an equally devastating hit in the long run), and focus on the interstate highway, which runs through Washington, Oregon, and California, linking Canada with Mexico.

When in place and operational, this road allows someone to get, for example, from Portland, Oregon to the LA basin, in one very long day of driving. But, if I-5 is closed, that route will no longer be available. And they WILL have to close it as far south as Sacramento and Stockton (or at least restrict the usage). One of the things that these types of volcanic eruptions produce — along with the shock waves and pyroclastic clouds and lava flows — are lahars.

A lahar is a volcanic mudflow that can flood downstream for a great distance, and cause all sorts of grief for those who get it its way, including massive loss of life and property. The lahar from Mt. St. Helens, for example, extended the whole way to the Columbia River, where I heard it dumped so much of Helen’s pulverized summit into the river that they had to bring in dredges so the ships stranded in Portland could get back to the Pacific.

Mt. Shasta — at 14,179 feet in elevation — has year-round snow and ice, and there will definitely be a lahar that will flow down the Sacramento River to San Francisco Bay. Imagine how much more exciting this part will be if the eruption happens in late-winter during the time of maximum snowpack…

(As an aside: The blue lake with several fingers just downstream from Shasta on the inset regional map, above, is Lake Shasta. If you were governor of California, would you drain the lake once the harmonic tremors start (and risk the multi-billion-dollar agriculture industry that relies on that water for irrigation) in the hopes of catching the bulk of the lahar, and thereby hopefully save the lower Sacramento River and S.F. Bay? Either way it’ll probably be a no-win decision: drain the lake and the state’s harvest may suffer and die. Don’t drain the lake and the displaced water will only add to the lahar. Governor? Not a hat I’d wanna wear.)

Let’s close the circle on our bedtime story: Pretend you live in Portland and want to take the kids to Disneyland. If the interstate is closed south of Mt. Shasta, your “one very long day of driving” just turned into two, or maybe even three, very long days of driving.

Now, the quickest and safest way to make the trip will be to take I-5 south to Grants Pass, Oregon, head through town to Highway 199, and then take that to Highway 101 in Crescent City. Be sure to stop at Dutch Bros (or the Human Bean) on the way by for some caffeine: you’re gonna need it. If you aren’t familiar with Hwy. 199, I am, and cannot even begin to imagine re-routing all of the I-5 traffic — trucks and Winnebago’s and all — onto that twisting, two-lane monstrosity that winds along the Smith River.

South of Crescent City it doesn’t get much better. Highway 101 wanders south through the coast range and what’s left of the redwoods until you finally hit San Francisco Bay. Unfortunately, there will be no way to get back to I-5 quite yet — they’ll have to close those roads as well because any massive eruption of Mt. Shasta would likely be devastating to the upper bay (“Better safe than sorry” will be the mantra of the year).

So, your only option would be to cross the Golden Gate Bridge (another traffic jam I have a tough time imagining), and stay on 101 until you get far enough south of the bay area to slide back over to the interstate (Hwy. 162 out of Gilroy would likely be your earliest reasonable route). Once you get back to I-5, you can resume your trip south to Disneyland. Be sure to give my best to Mickey and Minnie when you get there (and don’t forget to remove the gags from your kids’ mouths).

(Yes, I know: it would be possible to cross the Cascades from Eugene or Medford and eventually link up with Hwy. 395 that runs south on the east side of the Sierra. It’ll still take you two to three days (and possibly even four, depending on fate and fortune), but you’ll be able to skip going through San Francisco and Los Angeles, and come into D-Land from the northeast. Maybe take this route on your way home.)

Wanna have even more fun? Shift the scenario north to Mt. Rainier and consider the effect on the four and a half million people who live and work around Puget Sound (including Orting and Pike Place Market).

Mayor of Seattle? Not a hat I’d wanna wear…