|Mt. Baker and Boulder Creek upstream of Baker Lake Reservoir|
Vagabonding on Dangerous Ground primarily because we happened to be following the coastal parts of the Cascadia Subduction Zone which had become newsworthy over the summer because of a New Yorker article detailing the probable damage from an expect magnitude 9 earthquake offshore. Shaking, tsunamis, landslides, power disruptions and many other frightening events were part of the article. Kind of lost in the whole media affair were the sleeping giants that have always been a visceral threat to those who live in the region: the volcanoes.
In Cascadia the subducting slab of cold oceanic crust and underlying solid mantle material (the lithosphere) are driven into the much hotter asthenosphere, a "mushy" layer in the mantle that is partly molten. The interaction of the slab, water from the oceans, and the hot mantle rocks causes melting of some of the continental crust, forming magma that rises through the crust as a series of plutons. When they cool before reaching the surface, they will form visibly crystalline rocks like granite or diorite. When they reach the surface in a molten state, magma mayhem ensues.
Some lahars aren't even associated with volcanic eruptions. They can be triggered by landslides on the upper reaches of the steep cones, or by unusually high amounts of glacial melting (water trapped under the glacier may burst out all at once). Mt. Baker has the most snow and ice of any Cascades volcano except Mt. Rainier (and that's a big except, as Rainier has about 50% of all the ice in the lower 48 states). So lahars are the big danger from Mt. Baker.
nuée ardente, French for "fiery cloud". The good news in the case of Mt. Baker is that relatively few developments are close enough to the peak to be threatened. But there are some.
|Hazard areas in and around Mt. Baker in northern Washington|
Mt. Baker is one of the youngest of the Cascade volcanoes, having formed mostly in just the last 30,000 years. The last major eruptions took place around 6,600 years ago when large lahars swept down creek valley accompanied soon after by ash eruptions. The 1843 eruption was caused by a hydrovolcanic explosion (groundwater flashing to steam). That event left behind Sherman Crater. In 1975, there was a vast increase in the amount of thermal energy around the summit of the mountain, raising fears of an eruption. The heat subsided somewhat, and everyone forgot about Mt. Baker when Mt. St. Helens exploded just five years later.
|Lahar deposits at Boulder Creek near Mt. Baker|