A dynamic region: Cascades uplift shows our area isn't static

Registerguard.com ^ | Nov 3, 2003 | A Register Guard Editorial

[bicycle thug]

A 100-square-mile area around the South Sister is being thrust upward by an inch or two each year - too slow a change to be noticed in the course of a human lifetime, and too minute a motion to seem like more than a curiosity. But the uplift is occurring, as The Register-Guard's Karen McCowan reported in an Oct. 26 article, and it provides yet another reminder that our landscape is in a state of dramatic and potentially dangerous flux.

From a geologist's point of view, an upthrust of an inch or two a year is a big deal. Over the course of a century, that's eight to 16 feet - still nothing spectacular. But a yearly rise of an inch or two, sustained for 10,000 years, amounts to 800 to 1,600 feet. Ten thousand years is a very short period on the geologic time scale. The uplift is evidence that something dramatic is happening far beneath the surface of the Three Sisters area.

The uplift is believed to be the result of increasing volcanic pressure that could result in a lava vent, or even the birth of a new Cascades peak - a fourth Sister. It's not surprising that this should be so. Evidence of violent, and quite recent, geologic events is hard to miss in that region of the Cascades. The uplifting area itself has lava flows that are no more than a few thousand years old.

Fresh volcanic activity is found up and down the Cascade Range. The caldera that holds Crater Lake was formed 6,900 years ago. The caldera in Newberry Volcano holds the most recent obsidian flow in the world - a mere 1,500 years old. Mount Lassen, the southernmost peak in the Cascades, has hot springs and mud pots and has seen small eruptions in the past century. And of course Mount St. Helens exploded in 1980 and sent ash plumes into the air in several subsequent eruptions, leaving no doubt that the Northwest is a region of volcanoes.

Volcanic eruptions aren't the only violent events that are part of the region's recent history. Forces related to those that cause Cascades eruptions also trigger periodic earthquakes of great magnitude off the coast of Oregon and Washington. None of these big subduction-zone quakes has occurred since the beginning of the era of white settlement, but the geologic record is clear: They happen every several centuries, and the next one could be tremendously destructive.

Going a bit further back, the Northwest landscape bears the scars of periodic floods that occurred at the end of the last ice age. Water would build up behind ice dams in eastern Washington or Montana and then burst, sending a wall of water rushing down the Columbia Gorge. These Spokane-Missoula floods, fast moving and hundreds of feet deep, carried ice-trapped boulders halfway up the Willamette Valley.

If people had a 10,000-year perspective, they would see that the Northwest is the scene of continuing eruptions, earthquakes and floods. Instead, the human perspective is a few centuries long at most. The landscape is regarded as static, with such events as the eruption of Mount St. Helens being the exception. The challenge is to accept the geologic record as evidence of a need to plan and build with periodic violent events in mind. A couple of inches of uplift a year doesn't sound like much, but it's another reminder that this land seldom sleeps long.

[bicycle thug]

ping

[ValerieUSA]

The "plan" for human habitation in geologically active areas is for the survivors to relocate and rebuild following the next event. We are at the mercy of natural forces.