Monday, September 10, 2012

The Skies Near Mount Ranier

Located southeast of Seattle, Mount Rainier is the tallest volcano in the Cascade Range and the most topographically prominent mountain in the contiguous United States. Its summit is at an elevation of 4,392 meters and it has a topographic prominence of 4,027 meters. Because of this, many people from the Pacific Northwest are treated to the spectacular beauty of this snow-capped peak which dominates the landscape. But if you are really lucky, your view of Mount Ranier could be enhanced in some very unusual ways. 

A cloud shadow being cast from Mount Rainier. Photo by Nick Lippert.
   One way is by an amazing cloud shadow that only occurs with several factors happening concurrently. At the approach of winter, when the Sun rises farther to the south, it is possible for the first rays of light at sunrise to pass through a dip in the Cascade Range and catch the peak of Mount Ranier. If that sunrise is also accompanied by a cloud layer above the mountain, it will project a shadow onto the bottom of the cloud layer creating a spectacular cloud shadow. This could never happen in the Rockies because even though there are several peaks taller than Mount Ranier, none of them have the topographic prominence that is needed. And as the sun rises its light will scatter too much to cast a shadow behind it.

   Another strange yet beautiful cloud phenomenon that you can see near Mount Ranier is lenticular clouds. These are lens-shaped clouds that form at high altitude. Because of their smooth, saucer-like shape, lenticular clouds have been mistaken for UFOs. Lenticular clouds are formed when moist air travels vertically over the mountain and creates a standing wave pattern on the downwind side. Moisture condenses at the crest of the wave and evaporates at the wave trough, creating the characteristics lens shape. Even though the wind continues to move down the mountain, the lenticular cloud will remain stationary. Lenticular clouds can appear singly, or in clusters or stacks. Pilots will avoid lenticular clouds because of the dangerous wind shears that accompany them, but thrill-seeking hang gliders will use them to ride the wave for several kilometers.

A stacked lenticular cloud formation near Mount Ranier.
   At some point in the future Mount Ranier will give us the most-spectacular—yet terrifying—show of all: when it erupts. Even though Mount Ranier is quiet now and has been since the 1890s, geologists consider this stratovolcano to be episodically active, which means that it WILL erupt again at some point in the future. It’s for this reason, and the fact that Mount Ranier is located near a highly-populated area, that it was included as one of 16 “Decade Volcanoes” worthy of study in an attempt to reduce the severity of a future natural disasters. These Decade Volcanoes were studied as part of the United Nations International Decade for Natural Disaster Reduction during the 1990s.

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