During the El Niño of 1997-98, the western United States had record rainfall. For places such as Laguna Beach, with cliffs up along the coast, this could mean disaster. Unfortunately, at 12:30 am one morning it killed two people and blocked a major artery into Laguna Beach for months. Laguna Beach was not the only place that had a major landslide. Landslides were all too common up and down the coast as seen in the picture below. So, what did cause this landslide to happen?
Landslides occur when the land literally becomes full of water. Think of it like a glass of water. You fill it up to the top and you can go ever further to create a mini bubble. But, if you add a little too much, the bubble will burst and water will poor everywhere. The same happens to the land. The land soaks in the water, but when it is drenched with too much water it gives way. Water is dense. When all that weight is added to soaked rocks, it pushes toward the ground. Obviously, the land cannot move strait down because of existing rock, but it can move diagonally and give way. When this happens, there is a mini earth avalanche and all this debris can kill and destroy property.
There are four parts to a landslide. The scarp, head, body, and toe. The scarp is the top area where the land first gave way to. This is where the land is least stable below and most stable above. When the land does give way, it shows us what's inside the hillside. The head is the top part of the land that gave way, relative to the area around it. During the landslide, it is the part of the land that usually only moves downward, not outward. The head is normally not going to be in the debris field. The body is the saturated land that is moving downhill. This is the longest part of the landslide. Next, the toe is the small bottom part of the debris field that is rounded and clumped. This is the furthest extent of the landslide and larger rocks that build up here cause the lip shape.
So what makes this landslide so special? Well, Laguna canyon is made of the Monterey Formation. Inside this formation, you can expect to find siltstones and sandstone. Rocks that were made underwater. When the land uplifted, these rocks were dried out over millions of years. When the road was cut trough the canyon, the rocks were then situated on cliffs instead of a slope. When the el niño came in 1997, it was too much water for the dry rocks to handle so the rocks fell and created a landslide. This creates a natural slope up the hill, but blocks roads and destroys property so it must be removed. Only time will tell if and when another el niño comes if this canyon will be blocked off again.
Works Cited
http://landslides.usgs.gov/recent/archives/elnino/map.php#laguna
http://geology.about.com/od/naturalhazardsclimate/ig/Landslides/
http://scorescience.humboldt.k12.ca.us/fast/teachers/Mars/Tutorials/tutorial.htm
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1. Laguna Canyon Landslide on the first line of your email.
2. Describe the different features of the scarp you see in front of you. Also, describe the erosion procsesses that has been occurring since it was created in 1997 excluding the landslide itself.
3. Besides the scarp, why don't you see any of the three features of a classic landslide at this location?
4. Describe the landslide prevention techniques at this location and how they are being implemented here.
5. Do you think it's enough to prevent another landslide similar to the one in 1997 here? Are the prevention techniques likely to work in another el Niño season?
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