Sunday, April 26, 2015

Tahoe Highway Avalanche Control

Now that our driest winter in history is nearly over, it was a good time to get up on slopes that are normally buried in snow and check out what is used for avalanche control.

I was curious about Highway 50 where it comes down from Echo Summit.
This is the last big curve as you drive down from Echo Summit.
Just on the other side of that rock, up a thousand feet, is Echo Lakes.

In the old days, Hawley Grade was the rugged route from the far end of what we now call Christmas Valley up and over Echo Summit. It was the trail used by the Pony Express along with miners and settlers during the late 19th century. More about Hawley Grade in a future post.

The first modern road was what we now call Meyer's Grade. It was and still is a good road, although a bit steep for vehicles in the snow. It is now closed and used primarily by walkers. They only open it up for traffic when the newer highway gets closed by avalanches. Here are two posts about Meyer's Grade. Meyer's Grade hike and Meyer's Grade to Echo Lake hike.

Which brings me to this post.

The newer Echo Summit Highway (Hwy 50) was stretched out to make a shallower grade. The road, as you can see above, loops around under the rocky ridge that makes up the north side of Echo Lakes. Unfortunately, during snowy winters, the highway has a huge problem.


I met an old-timer at a book event, and he explained it to me. Back when the newer road was constructed, in the 1950s or '60s - I forget - he worked on the crew that designed and built the highway. He said they'd laid out the entire route, focusing on the percent of grade, the drainage, and all the other stuff that highway builders concentrate on. They were well into the project- too far in to make changes - when someone looked up at the massive slope of smooth rock above the road and said, "Gosh, I bet this is one of those places where snow slides pretty easily."

Talk about an understatement.

The Echo Summit highway is one of the worst for avalanches anywhere. Smooth, steep rock rising up thirteen hundred vertical feet in an area famous for massive snowfalls. For example, in the winter of 2010-2011, Echo Summit received around 700 inches of snow.

The result is sometimes continuous avalanches. At times, the avalanches will bury the highway 20 feet deep in heavy compressed snow. To keep the highway open requires serious avalanche control. (For comparison, the slopes above the Old Meyer's Grade are forested, and trees are very good at holding snow in place.)

The basic process is this. Instead of waiting for massive snow pack to build up and possibly release in a catastrophic slide, they create frequent, smallish, man-made slides. After a storm, Caltrans closes the highway so no one gets hurt, then they use a range of ways to make the snow slide.

The main one is air cannons. We hiked from Echo Lake, over the ridge to take a look at them.
Note the Echo Summit Highway down below in both pictures

They are called Gazex cannons. Made by a French manufacturer TAS, they consist of a big curved pipe, which is filled with a mixture of propane and oxygen. The operator, sitting in an office in Meyers, runs them from a computer. When the signal is given, the gas is ignited, and it explodes in a serious percussive Whump, directing the blast down at the snow. The shock wave is significant (You can hear it miles away - it sounds like an artillery explosion or a sonic boom) and the blast releases any snow that is ready to slide.

Gazex exploding to release a controlled avalanche

There are several of these Gazex cannons spread across the rock face above the highway.

But what if they aren't enough?

At the bottom of the slope is a Gun House that has a LoCat-type cannon that is operated by compressed air. It shoots an explosive projectile up onto the slope. The projectile explodes and releases the nearby snow.

Zooming my camera lense from above, you can just see the Gun house in the picture. It sits near the bottom of the rocky slope.

The Avalanche Gun House up close

Behind those green doors is a compressed air cannon. After a major snow storm, the cannon can be pointed at any problem area on the slope above to shoot down the snow.

Most of us tend to take clear highways for granted. But keeping them clear is a big deal in snow country. 

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