Our Northwest

Proof of Rainier’s past grandeur plain to see

Wednesday, April 16, 2014by  Jon Osterberg

Bright sunshine and blue skies reigned recently, and we’ve been gawking at our Mountain.
   When Puget Sound locals say “the Mountain is out,” we mean you can see Mt. Rainier. We don’t take that for granted, thanks to our abundance of gray clouds.
   Rainier remains spectacular, even to those familiar with it. Though exceeded in height by Mt. Whitney in California (14,497) and Mt. Elbert in Colorado (14,433), Rainier stands out far more. Whitney and Elbert rise just a few thousand feet above their surroundings, while Rainier soars from the Puget Sound lowlands – nearly sea level – to 14,411 feet.
   When viewing Rainier from the north, a conspicuous craggy spire stands out on its east flank. Little Tahoma, which rises to 11,138 feet, offers a hint of even-greater grandeur in Rainier’s past.
   Little Tahoma (left) is a remnant of Mt. Rainier’s original east flank, since eroded.
   Draw an imaginary line that follows Tahoma’s general angle upward from its tip. (See top photo; peak in distance is Mt. Adams.) That line points to Rainier’s former summit.
   Geologists know that in the past, Rainier rose far higher than today. It likely was symmetrical, perhaps resembling pre-1980 Mount St. Helens. Then an explosive eruption blew away the upper 2,000 feet of Rainier’s original volcanic cone.
   Some people mistake Little Tahoma for a “parasitic cone,” a volcano that emerges from the flanks of an older, larger one. Mt. Shasta in California has such a cone on its shoulder, called Shastina (right).
   But Rainier's behavior more closely resembles St. Helens, which famously blew 1,300 feet off its top in 1980.
   Another Cascade volcano, ancient Mt. Mazama, lost its top about 7,600 years ago. But Mazama’s top didn’t explode as much as it collapsed on itself. Today we know the lake that fills the huge caldera as Crater Lake (left)
   But I digress.
   Geologists believe Mt. Rainier formed about 500,000 years ago. Around 5,000 years ago, a massive avalanche of rock and ice broke loose, causing the Osceola Mudflow that reached present-day Tacoma and left Little Tahoma as an isolated remnant of Rainier’s east flank.
   That’s something to keep in mind while gawking at Rainier on a blue-sky day. Rainier is a dormant, not extinct, volcano. Eruptions and lahars – destructive mudflows caused by hot lava – remain a threat.
   And Little Tahoma reminds us of Rainier’s restlessness.

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Comments on this post

personGale S. Kennedy05/03/2014 07:46 PM
As a survivor of Mt. St. Helens' eruption on May 18th, 1980, I have some advise for everyone when Mt. Rainier performs her skyward projectile vomiting. RUN!
personDY04/18/2014 10:20 AM
Whenever I stand on the rim, it's amazing to imagine it was once a symmetrical 12,000 ft snow-capped sibling. Mazama translates to "mountain goat" BTW.

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