Impacts of Climate Change on the Pacific Northwest

August 21, 2019

Geology Blog 1: Volcanic activity in PNW


We are undergraduates from Nanjing University. In this summer workshop, we’re focusing on the geology of Washington. Our majors are very different, including GIS, human geography, marine science, atmospheric science.

Geology team: Zhao Dayang, Xu Rui, Wang Luhan, Bao Yang, Zhang Jiangyi

Before we went hiking on Mt. Rainier, we watched a video about Mt. St. Helen’s eruptions. They are both active volcanoes, but the last time Mt. Rainier erupted is uncertain. Through the video, we had a general understanding on how destructive the eruption of Mt. St. Helen was, but the fact that Mt. Rainier is bigger, an eruption of Rainier could be even more devastating. This is the reason why our leader teacher said after watching the video, we may feel scared to hike there. However, attracted by fascinating landscapes, we forgot that threat.

Mt. Rainier

Mt. Rainier is an active volcano with an elevation of 4367 meters. The bedrock of Mt. Rainier is mainly composed by granite and the volcanic body is mainly composed by Andesite. It is a subduction of the Juan de Fuca Plate and North American Plate. The basic characteristics of Mt. St. Helens is similar to Rainier except that the elevation of Mt St. Helens is 2550 meters.

Mt. St. Helens

After several minutes of gondola ride, we reached the summit where we saw Mt. Rainier and Mt. St. Helen’s clearly. Some of the differences we noticed between the two mountains were:

  • There was a lot of snow and glaciers on the foothills of Mount Rainier and above, while Mount St. Helens had only a small amount of glaciers or snow covering on the top of the mountain.
  • The top of Mt. Rainier is more regular than Mt St. Helens which has a gap.
  • There is a large difference in their elevation.

For Mt. St. Helen’s, the large landslide caused by the volcanic eruption reduced the elevation of the mountain from 2,950 meters before the explosion to 2,550 meters, and formed a horseshoe-shaped crater 1.5 kilometers wide and 125 meters deep.

Mt. Rainier and Mt. St. Helens

At the summit, we overlooked a winding river filled with white water, which accounts for its name, white river, originating from Emmons Glacier on the northeast side of Mount Rainier. The white river travels along the path of the Osceola Lahar according to the map given. We guess that the Lahar caused the river which is distinctive compared to the flourishing trees on its banks. Lahars are extremely destructive for the speed can be up to several tens of meters per second and it can damage any structure or vegetation it comes into contact with. However, we learned at the geology museum located in the visitor center, volcanic ash is one of the most dangerous product of Mt. Rainier. Ash makes it difficult to breath and see as well as ruins crops. From courses related to atmosphere, we know that with the ash and debris flowing into stratosphere, the initial radiation balance will be broken, and then the land below becomes cold. This way vegetation may die or get weak without sufficient sunlight.

White River

All in all, we did enjoy the spectacular mountains and milky snow glaciers etc., however, what impressed us most were the history of eruptions, how they formed and how they impact ecosystems and people.