I’m taking a quick breather from the heavy science stuff to highlight one of my favorite features of the area around Portland, Oregon, where I live: the amazing extinct volcanoes. There are at least 32 in the Portland metro area. Oh right, well maybe this will involve a little bit of geology, which is science I suppose. Sorry ’bout that.
The volcanoes, which were active up until about 300,000 years ago, are cinder cones and generally small shield volcanoes (like in Hawaii, except those are BIG shield volcanoes). Many lie within the city limits, and several have city parks covering their summits. I happen to live quite close to two of them: Rocky Butte and Mount Tabor. Both have parks, but the one at Mt Tabor is much more extensive, with hiking trails, tennis courts, a large playground, picnic areas and more. There is even a natural amphitheater at Tabor where live music is often hosted on warm summer evenings. This popular venue occupies the volcano’s old explosion crater. How cool is that?
While each of these old volcanoes in Portland have their own character and personality, one stands out above the rest. It is the king of them all, a looming hulk over 4000 feet (1240 meters) high on the east Portland skyline. I’m speaking of Larch Mountain. There are no larches on this well-forested shield volcano, so one might wonder how it got its name. Early lumbermen sold noble fir from the mountain and labeled them “larch”. How come misnomers so often stick?
Larch is quite a large mountain, but most people do not take notice of it at all. Beyond Larch Mountain lies the Cascade Range, with big snow-capped peaks like Hood and Adams. These more dramatic peaks draw the eye away from foreground mountains like Larch in Oregon and Silver Star in Washington. But try to ride your bicycle up Larch’s 16-mile long road, and you quickly discover how big this mountain actually is. Like most shield volcanoes (named for their resemblance to a shield laid concave side down), Larch can easily escape notice. This is because they are so broad, with gentle slopes. And the gentle slope is because most of what pours out of a shield volcano during eruptive phases is a very liquid form of lava – basalt. Basalt is the hottest and most dense lava on Earth, and it covers most of the ocean floor. Because of its relatively low silica content, basalt flows very easily, forming smooth shallow slopes and a broad volcanic edifice.
Copious quantities of basalt flowed out of Larch Mountain’s summit vent during the early ice ages. It’s part of what geologists call the Boring lava field. The name does not describe geologists’ feelings about this very interesting volcanic feature. Rather the name comes from the little town of Boring, which is southeast of Portland. The volcanoes are actually quite interesting because of their position far to the west of the main axis of volcanism represented by the Cascade Range.
Whenever my eyes drift up toward the east, I’m always impressed by the sheer bulk of Larch Mountain. In certain light conditions it is almost lost, but in other light you can get an accurate feel for how dominant the mountain really is. The views from the top are absolutely stunning. You can look east to see an interesting angle on Mt Hood, north to see Mounts Rainier, St Helens and Adams in Washington, or west down the length of the Columbia River. I often ride my motorcycle up there for sunset when the road is open (snow closes it in winter). And stargazing from the summit is quite excellent, despite the proximity of Portland’s light pollution.
If you ever find yourself in Portland and want to catch the sunset from a high viewpoint, make the drive up to Larch Mountain. Just head out the Historic Columbia Highway from Troutdale. Not far past Corbett, and just before you come to Crown Point, you will see a sign where the road angles up to the right. Don’t forget your camera!