JOHNSTON RIDGE OBSERVATORY, Skamania County — It's hard to stand here and not feel the absolute, raw, up-through-your-boots power of a volcano.

Mount St. Helens is five miles away but fills the view. Its top is clearly missing, slumped and blasted away on May 18, 1980. The landslide that fell off its side easily rose hundreds of feet to sweep over part of this ridge.

More than 20 years later, the surrounding ridges and river valleys are a blasted and scoured diorama of the dawn of earthly time.

But the drama of the mountain's last explosion shouldn't get all the ink. Mount St. Helens is only the latest and most visible pop star to rise out of the state's volcanic history. It is a scene-stealing and sassy upstart, a youthful media darling whose brashness and celebrity obscure a long line of great acts.

Washington state has four other significant volcanoes — nearby Mount Adams and, starting from the north, Baker, Glacier Peak and North America's most dangerous volcano, Rainier.

The volcanic processes that churn beneath these snowy beasts have had an outsized role in making the state what it is. A glacier carved out Puget Sound and created the deep-water port of Seattle, but volcanism has had a huge role in building the divide of the Cascade Mountains and the arid plains to the east.

"It's a rainfall divide, which makes for a settlement divide, which makes for a political divide," said Ralph Haugerud, a University of Washington geologist. "There are so many ways that volcanism makes a difference."

"If you look at what influenced the state in the past 100 million years, it's definitely volcanism," said Steve Reidel, staff geologist at Pacific Northwest National Laboratory and a geology professor at Washington State University-Tri Cities.

But it only goes so far, said Peter Frenzen, Mount St. Helens National Volcanic Monument scientist.

"Mount St. Helens was a relatively small event," he said. "It kind of puts in context the forces that were involved in the shaping of Washington state."

The surface of the Earth builds itself up and tears itself down, its thin crust rending, subducting, melting and reforming as it floats across the globe. A lot of that happens here.

About 700 million to 800 million years ago, the oldest known supercontinent, Rodinia, split around the Tri-Cities, with North America getting born to the east and the Pacific Ocean forming to the west. About 240 million years ago, a conveyor belt of rock started a slow-motion slam into the coastline. Some went beneath the continent to melt and resurface as magma, and some piled up against the coast, creating the Cascade Mountains.

Most of the mountain range is not volcanic, but the molten rock below floats up as it cools and congeals, lifting the Cascades.

Were this not happening, Snoqualmie Pass could be sitting at about 500 feet, not its current elevation of 3,022.

And the arid plains of Eastern Washington would be a far greener place.

"The Evergreen State would be evergreen across the whole state," said Donald Meinig, geography professor at Syracuse University and author of "The Great Columbia Plain, A Historical Geography, 1805-1910." "It would be just like Western Europe."

Seattle would be colder and snowier, too, with frigid air from the interior of the continent no longer blocked by the Cascades when it moves west, said Cliff Mass, a University of Washington meteorologist.

Forests, fish, dams, water supplies, hydropower and mountain skiing all would be altered.

Just as magma has made the high peaks higher, it has made Eastern Washington flatter. Between 11 million and 15 million years ago, large fissures between Spokane and Lewiston, Idaho, produced lava floods of biblical proportions, with hot rock flowing across Eastern Washington and Oregon and down the ancestral Columbia River gorge. In Pasco, a drill will go through 300 feet of sediment then 4,000 feet of flood basalt before hitting older sediments, said Reidel. Oddly, some of the best evidence of a lava flow's power is found on Mount St. Helens, which Frenzen describes as a switch-hitting volcano: It can blast you sideways with ash and gas or smother you slowly in liquid rock.

"If you're out here, you have to watch where you walk," said Frenzen, the monument scientist, as he set out to stroll through the Trail of Two Forests. A boardwalk makes for easy going, and the rock has long since cooled. But on either side are deep, natural manholes created as lava flowed through an old-growth forest 2,000 years ago, surrounding 4-foot-diameter trees that acted as molds for the cooling rock.

At one point during the boardwalk's construction, inmates from the Larch Correction Center found a tunnel, created by a fallen tree, leading from one manhole to another some 40 feet away. No one escaped, but the boardwalk was rerouted to include the feature.

The ultimate tunnel is the nearby Ape Cave, created when the outer layers of a lava flow cooled and hardened, forming a tube for the lava within. It is the longest lava tube in the lower 48 states, stretching for more than two miles. And within feet of its dim, ferny entrance, it becomes dark and cold and nearly lifeless save for bacteria and fungi on its walls and the tens of thousands of lantern-toting hikers who visit each year.

"Think of this full of several-thousand-degree rock kind of cruising down here, molten," Frenzen said as he walked along the cave's uneven floor. "You can imagine what the Columbia basalt flows were like. This is a small-scale version of that kind of thing."

"It must have been spectacular to watch, just like we're mesmerized by watching the Hawaiian lava," said Patrick Pringle, geologist for the state Division of Geology and Earth Resources. "Just like the geologists say when you are going to Hawaii, you're going to see red rock. It's such a big deal."

But back up on the surface, the modern-day Mount St. Helens still makes a case for being the state's most impressive volcanic feature. Even on the less-impacted northeast slope, away from the force of the mountain's landslide and pyroclastic blast, one can see where Shoestring Glacier was decapitated by the 1980 eruption, creating a slurry of mud and rock that cut a wide swath to the east.

"I think they figured it was going 100 mph," Frenzen said. "It scoured trees and blasted them over."

But those who would forget the rest of Mount St. Helens' history would do well to consider that the mountain may have been active for some 120,000 years. Just 3,500 years ago or so, it kicked out a plume of yellow rock, lava and ash 12 times greater than the 1980 eruption. Writing in his roadside geology of the mountain, Pringle said geologists compare that eruption to Italy's Mount Vesuvius, which buried Pompeii and Herculaneum in 79 A.D.

The eruption appeared to bury local Indian settlements as well. Archaeologists for the Gifford Pinchot National Forest have found that sites affected by the eruption went unoccupied for between 1,000 and 1,600 years. The ash could have been six feet thick, destroying plants on which the natives depended.

There may also have been a taboo against living near the mountain, said Rick McClure, a Gifford Pinchot archaeologist. Oral histories and traditions talk about the area, particularly Spirit Lake, which was created by the blast of 3,500 years ago, as a place you didn't go.

The salmon in the lake were the spirits of dead warriors and weren't to be taken. An ancient chief spirit in the form of a huge lion lived in the forest.

It lives here still, in the forest and in the hot rock trembling beneath our feet.

Eric Sorensen: 206-464-8253 or esorensen@seattletimes.com