Welcome to a nice little roadside parking area. Immediately across the four-lane highway you can view where a major landslide occurred a few years ago, and you can also see what the state highway department has done to mitigate (prevent) future landslides. Thanks to Google Maps, we can get a clearer picture of the dramatic changes a landslide can have. This EarthCache presents an unique opportunity to see both before and after the landslide has occurred, which brings into focus how devastating a landslide. But first, let’s learn about landslides.
Note: There is no requirement to cross the road or venture onto the mitigated slide area. If you choose to inspect this area, please wear appropriate protection including a hard hat, safety shoes, gloves and safety glasses.
What Are Landslides?
Landslides are one of the most dangerous natural wonders on Earth. Landslides occur when land, rock, and debris plummet down the side of a mountain or cliff, sometimes at breakneck speeds.
Landslides can be found all over the world, including every state in America. They can occur on every type of surface, whether rocky or sandy, and also happen both on land and underwater. There are many causes of landslides, some natural and some man-made, and the effects can be minor to severe devastation.
How Are Landslides Formed?
In order for a landslide to occur, three factors have to work together:
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An unstable subsurface (subsurface is the land just below the Earth's surface), which can be caused by natural or human causes. Natural causes include overly saturated ground and erosion of topsoil. Human causes include deforestation of land and even over-farming or over-building.
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A trigger, which is some event that causes the landslide to start. Triggers can also be natural or man-made. Earthquakes and volcanic eruptions are both examples of natural triggers. Human triggers can include vibrations from heavy machinery or traffic as well as blasting, which is the use of explosives to break rock or other hard surfaces.
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Gravity, which is the force that pulls objects down toward the Earth. Once you have unstable land and a trigger, gravity will do the rest of the work during a landslide.
Mitigating A Landslide
In order to prevent (or mitigate) a landslide, one might use one or more of the following actions:
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Excavation
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Strengthen the Slopes
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Plastic mesh reinforcement
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Rock fill at the base
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Creating a channel for drainage
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Fencing, wire nets, and cables
Across the road from these coordinates, you will see where a large landslide occurred that was triggered by a heavy rain event in February 2020. The stabilization and cleanup project took roughly 6 months to finish. One lane of the highway was closed during this time.
2015
Signs are prevelant from past slides. Concrete barriers in place to keep material off of road, and slides visible in background. A large area underneath the power lines is kept clear of trees and shrubs.
2016
Slides at the top of the ridge are becoming more pronounced.
2017
Vegetation, trees, and ground cover have been diminshed.
2021
Very dramatic change with tons of earth removed. The powerlines have been moved to the opposite side of the road as well. Notice how large the underlying bedrock is, and the angle of it. With the top, shallow layer of soil and debris removed, it's easy to see how a slide could occur.
In order to complete this earthcache as a find and collect your smiley, you must complete all requirements below. Failure to comply will result in your log entry being deleted.
Please send your best answers to the following questions:
1. What could have been done to prevent the landslide from occurring?
2. What "triggered" the landslide discussed above?
3. Name a mitigation technique that has been used at this site to reduce impact from future landslides.