Speaking of pumping....
Mt St Helens created a huge problem when the eruption lahar & debris avalanche dammed up Spirit Lake below. The lake became a giant with thousands of blown down logs forming a “giant mat” on the lake surface.
pics at article: http://www.amusingplanet.com/2015/01/a-gigantic-mat-of-floating-tree-trunks.html
This giant debris dam was unstable and had to be emergency pumped to safe levels. They anticipated the lake would overtop its ashen based material and then release a mudflow that would bury cities 40 miles downstream (Toutle River into the Cowlitz river). The Army Corp of Engineers did a herculean job in setting up some monster pumps. The head of uplift was amazing to get the water up and over the nearest ridge from the lake (into a separate watershed).
The corp built a remedial “mitigation dam” to help control the surges of runoff from winter rains and help protect the levy systems in the towns of Kelso and Longview.
The permanent solution to preventing this avalanche dam from bursting was done by building a tunnel through a mountain to the lake to continually drain it at a certain elevation.
Recently, the tunnel had to have emergency repairs performed as the tunnel was mysteriously narrowing. They stated that “the earth shifted” in causing this narrowing. Keep in mind, this tunnel was bored/cut in rock. Thus the “tunnel floor shifting upward” is not a good sign. (btw- Mt St Helens is starting to come back to life in activity - magma is stated to be moving up).
I monitor the volcanoes in the PNW. Mt St Helens is beautiful. It has a natural spring that is amazing. It is just like a small pristine river flows out of the base footing of the mountain - Kalama River. I’ve been near the headwaters of the spring to get water samples for sulphur & mineral testing. For fun, I did a few “whoop” calls to see what might respond.
The herds of Elk are amazing. They flow up mountainsides with grace and speed that I couldn’t even stagger up. At the top of the ridge they just looked down at me like the scenes in movies where natives are perched all along a sight ridge....
=== Article clip
http://www.usatoday.com/story/news/2015/05/14/mt-saint-helens-volcano-spirit-lake-tunnel-overflow/27326173/
PORTLAND, Ore. — A tunnel dug to help drain a lake whose natural outlet was blocked when Mount St. Helens erupted in 1980 is narrowing. Experts say if it fails, Interstate 5 in Washington state could be inundated.
The Spirit Lake Tunnel was built after the 1980 Mount St. Helens eruption, when ash and debris blocked the lake’s natural outlet into a local creek.
When lake levels began to rise, the U.S. Army Corps of Engineers bored a 1.6-mile tunnel through bedrock to provide Spirit Lake a new outlet.
The tunnel opened in 1985. Last fall and spring, inspections found that the tunnel floor was rising. Geologists say shifting rock formations under the surface are to blame.
A tunnel through the middle of an active volcano? Hmm, not too sure about that one. I guess part of the next eruption might spew laterally like a horizontal spigot spewing molten lava. Wouldn’t want to be in the way of that one.