Continuing phreatic (steam) blasts opened an even larger crater than the one opened March 27, 1980 (behind and front, respectively). Though I probably didn't understand at the time what I was seeing, it is now blatantly obvious to me that this is tensional fracturing as the north side of the mountain bulged out (view above is to the west). Reduced to simple terms, perhaps too simple, a slab on the north side of the mountain is hinging upward and outward as a magma body shoves toward the summit. The rock, ice, and snow of the summit is being pulled apart between the "stable," more-or-less fixed, mountain block to the south, and the outward flexing, unstable, slab on the north face. Below, you can't see the structural details, but you can see the ominous black coating of pulverized rock on the south slope, and Mt. Rainier in the northern distance. (Both pictures, dated 3/30/80, from the USGS photo archive.)
I took a couple of minutes to scribble up a geo-cartoon to more clearly illustrate the activity discussed above with respect to the first photo:
As I said in the previous St. Helens post (first link above), I was enthralled. It's hard to remember, 30 years after the fact, how much I really understood at the time. I had had an interest in geology since childhood, and a fairly weak earth science class in high school, but from my current point of view, I was pretty much geologically ignorant and naive. But I was interested and I was paying attention. And that's a very good position to start from.The piece that reminded me that I wanted to return to this retrospective of what we (I) knew and when, was another retrospective by Mike Beard in today's Oregon Live recalling how he just happened to be in an airplane watching the mountain the day it had its first blasts, March 27.
The "scoop heard 'round the world" wasn't the result of hard-nosed journalism. It wasn't because the reporter was especially tenacious. It wasn't even the reporter's best work -- far from it. No, the scoop occurred because, frankly, the reporter happened to be in the right place at the right time. I know this because I was the reporter.(...)
Our small plane lifted off from Pearson Field and burst through the heavy cloud cover to emerge into a sunny sky. It was almost immediately apparent to the pilot and me that something unusual was occurring -- St. Helens' snow-covered cone was darkened as if by a cloud. Minutes later, as we drew closer, we realized with wide-eyed excitement that we were witnessing an erupting volcano; a crater had opened, steam was venting and ash was drifting down the pristine, white slopes. Best we could tell, we were the only ones in the air. Because of the low cloud cover, no one on the ground could possibly see what we did.Some guys have all the luck.
I grabbed the two-way radio and called the station, only to be greeted by silence. Erickson was at lunch! Eventually, the disc jockey turned down the Beach Boys and answered the two-way.
"Stop the music! Put me on the air," I hollered. Instead, he summoned Erickson from the cafeteria. Via two-way, Erickson asked me to describe what I was witnessing. Then he asked me to repeat myself, slowly. "You'd better be right," he said, suggesting that I'd be looking elsewhere for work if I wasn't. Signaling the DJ to break into the programming, Erickson had the presence of mind to speed-dial the local Associated Press bureau. "This is Erickson at KGW. Turn on the radio," he said, slamming down the phone as I began describing the scene unfolding just below our small plane. The AP transcribed the report directly off KGW's airwaves, simultaneously flashing the story into newsrooms around the world.
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