Mt. Rainier

by Amy Appleby

Hazard Maps

(a class assignment, not for real use)

       A Tephra Hazard Map of Mt. Rainier

      Red-- (meters thick) Extremely dangerous and should be completely evacuated

      Blue-- (1-5cm thick) Highly dangerous, little to no visibility, danger to structures

     Green-- (.5-1cm thick) Dangerous, poor visibility, extensive damage to crops

       There are three zones of danger in terms of fall out from an explosion of Mt. Rainier. The Tephra would generally favor the east because of the dominating winds. The range of fall is quite small for a volcano like Mt. Rainier, especially when compared to the range of fall out from Mt. St. Helens. However, any sort of eruption column and fall out can severely damage aircrafts and therefore there needs to be a wide no fly zone.

       The red zone is the most dangerous with large falling ballistics that could be as large as 10s of centimeters across and create a layer several meters thick. These hot pieces of Tephra could start fires and would cause death or serious injury on impact. This would be an area that would be extremely dangerous to be in during an eruption, not only from the fall out but also from the many other hazards such as Pyroclastic flows and Lahars.

       The blue zone is still highly dangerous and would considerably disrupt life within it. However, unlike the red zone, the tephra would be resembling fine ash rather than larger pieces of pumice. This can be even more dangerous as it is capable of completely blocking out light and reducing visibility to a few centimeters. This can cause devastation to structures as even a layer of 5cm could collapse a roof, public water and sewage systems could be overwhelmed by the fine material and fail, and people's respiratory systems can  be at risk.

        The green zone is capable of getting .5-1cm of ash. There is still poor visibility for these areas, and therefore impossible to safely drive in. The public water and sewer system can still fail from the inability to process such fine ash. But the largest and most long-term issue is the damage to crops from fall out. Even a small layer of ash can wreck a crop for a season. The clean up required will similarly take up time and resources for weeks after the eruption.

 

      Lahars and Pyroclastic Flows Hazard Map

      Red--Highly Dangerous area prone to Pyroclastic Flows, Surges and Lahars

      White--Possible primary or secondary Lahar flows

      Green--Possible Flood areas caused by Lahars  

      The most dangerous hazard that Mt. Rainier can produce is a Lahar: fast moving (10-60 km/hr) debris and mud ( most commonly created by melted snow and ash at Mt. Rainier) flow. It is capable of carrying boulders the size of buses hundreds of kilometers from the vent. The consistency is similar to cement and tends to be devastating to wherever it travels . The largest Lahar in the world's history was produced by this volcano on top of which many towns are now built . The Osceola Mudflow occurred 5,600 years ago and covered an area of 550 km squared reaching the southern Seattle suburb of Kent and the current Port of Tacoma XII. Secondary Lahars can also be triggered months after an eruption. If enough ash has accumulated on top of a ridge, and there is a large amount of rainfall, this can create a Lahar that will travel down channels and rivers collecting more debris as it goes. Similarly, if Mt Rainier emits hot gas or the volcano starts to warm up, then the snow and glaciers on top can melt and create a Lahar. Secondary Lahars are often more dangerous than primary ones as many people can be unprepared since there is no eruption to force people to get ready.

        The Red area is highly dangerous and should be off limits to everyone. This is an area prone to Pyroclastic Flows which are extremely hot (570 degrees Fahrenheit) and are very fast (200miles/hr). Due to their temperature, they can melt the snow and glaciers and turn the Pyroclastic flows into Lahars. This entire vicinity will prone to all sorts of volcanic hazards in which no one would be safe.

        The White areas are possible paths that primary and secondary Lahars could take. They all follow deep river valleys which would cause the Lahras to pick up even more water. In this map I have created the worst case scenario. Only if Mt Rainier has an large Plinian eruption with a VEI of 5 or 6 will these Lahars probably be able to reach the port of Tacoma, many will settle further upstream.

        The Green is possible flood areas that these Lahars could create. Not only do the Lahars themselves contain a lot of water, but they can break damns and block rivers. The low lying flat areas in and near Tacoma and its surrounding cities would be prime examples of where water may collect. Further up the Lahar paths, however, the valley walls are too steep and therefore most likely any flooding would be contained and not be too devastating. It is only close to farm lands and bodies of water that floods would be a large hazard due tot he leveling out of topography.

 

   
Questions about this site? Contact me aappleby@mail.colgate.edu