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Background Information
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gscmaplajollaslide.jpg


On October 3, 2007, a hillside began to move just before 9:00 am., causing a large landslide on Soledad Mountain Road in La Jolla.
A landslide is a natural disaster that occurs when there is ground movement, which causes rocks to fall, land to give way, and failures of slopes. There are many factors that combine to cause a landslide, but something usually happens to trigger the actual landslide depending on which type of landslide it actually is. The landslide of La Jolla that occured in October 2007 happened on Soledad Mountain Road just off the 5 Freeway near Palomino Road (as marked by a red star in Figure 1 on the left). It did have small warning signs that caused officials to warn residents of the area in case something did happen.111 homes, valued at millions, were evacuated off the hillside. However, the damage caused by the landslide was not predictable and led to major losses to several people in this area. This type of landslide is considered to be a Rotational Slide (as seen in Figure 2), which consist of homogeneous, cohesive, and soft materials that lack a planar surface. These slides often slide on a curving slip surface which concaves in. As the mass moves down, the land can slightly rotate and collapse.
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rotationalslide-1.jpg
The lowest part of the mass moves outward from the slope and excess material above the original surface may collapse and cause a debris slide. Rotational slides tend to happen more often in coastal Southern California and it happened at Mount Soledad because weak materials formed this portion of the area.



Warning Signs and Consequences


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cracksaugust2007.jpg
Warning signs of this landslide in La Jolla started around July 2007 when residents started noticing and reporting cracks in the pavement of Soledad Mountain Road (as pictured in Figure 3 on the right). When San Diego officials determined that these cracks were developing due to geological settling, they decided to begin monitoring the area. Earlier in the year, as recent as July the city began noticing cracks on Soledad Mountain Road and gas main breaks in August. Then shortly after in September a waterline in the neighborhood was replaced with an aboveground pipeline to prevent damage from moving earth.
A La Jolla resident, Erinn McCormick, comments that she had called city officials for many before prior to the slide occurred about a water leak on her street but that she did not receive a response until only two days prior to the slide. Even with all the geographical warnings, there seemed to be a general disregard to the impending slide. Reportedly, slides in this area have occurred between 1961 and 1994, with a major slide in ‘61 that destroyed seven homes under construction. On Tuesday, October 2, 2007 there was an increase in instability of the land and luckily officials warned residents of four homes to evacuate because it was unsafe, as these four homes ended up sinking down the slope the next day.
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lajollaslidediagram.jpg
The next morning, a slab of the mountain began to slide, which is shown in Figure 4 to the left. After this large selction of slope started to slide, just hours before the complete collapse, a firm the city hired a month prior, installed mesasuing devices. However, this research came a little to late and the hillsides collapse cut a 20 foot deep fissure into the hillside. There were several factors that contributed to the failure of this slope according to geologists including soil composition, effects of a nearby fault, and surface impacts of development. This collapse caused a 200 foot stretch of Soledad Mountain Road to buckle and cause a landslide below (as seen in Figure 5). As surface soil collapsed and the road buckled, it damaged homes and caused soil to continue sliding below. After this landslide occured on Wednesday, October 3, 2007, Governor Arnold Schwarzenegger declared San Diego in a state of emergency since the landslide had caused over $48 million in damages. Damages included $26 million in public works damage and $22 million in property damages. Fortunately there were no injuries or fatalities due to this landslide, but it caused closure of Soledad Mountain Road and destroyed two homes. Other homes suffered damage, including
severe structural damage, as well as damaged power lines and minor gas leaks.How shuld they go about fixing the cause? San Diego State University geology professor Pat Abbot was quoted saying, ”… all repairs that have been done [since 1961] have just been “Band-Aids” and that the only way to truly fix the problem is to to tear down all the homes in the area and start over.”In all, there were three roads considered impassible for a short period of time, fifty five homes
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damageonsoledad.jpg
evacuated, and fifteen left uninhabitable. The main damage of this landslide is pictured to the left in Figure 5. Displacement of the slope and street can easily be seen, but the other damage that was caused by this landslide does not appear in this picture. This disaster caused a lot of damage that seemed as if would never get completely repaired. In fact, some geologists said that this damage could not be completely fixed unless everything was torn down and construction started all over again because the slope would need better support due to how it was formed from the weak materials of the Rose Canyon Fault. This devastation that the La Jolla Landslide has caused has made officials more aware of problems in the Los Angeles area that could occur and result in a similar landslide. Therefore, certain cautionary movements should be taken in order to prevent damage that can be avoided.






Resources


1. Hyndman, Donald and David Hyndman. Natural Hazards and Disasters. 2nd Edition. Brooks/Cole, Cengage Learning: 2006.
2. Sauer, Mark. "Landslide in La Jolla." Union Tribune. [Online] <http://www.signonsandiego.com/news/metro/20071004-9999-1n4slide.html>.
3. "Governor Declares State of Emergency in Wake of Slide." San Diego News. [Online] <http://www.10news.com/news/14260985/detail.html>.
4. Ohlman, Micah. "La Jolla Slide Focuses Attention on Danger to Hillside Homes." ABC News. [Online] <http://abclocal.go.com/kabc/story?section=news/local&id=5691661 >.
5. Morris, Regan and John Holusha. "San Diego Landslide Threatens Homes." New York Times. [Online] <http://www.nytimes.com/2007/10/03/us/03cnd-slide.html?_r=1&hp&oref=slogin>.
6. Hoffman, Allison. "Residents Return After La Jolla Slide" Washington Post. [Online] http://www.washingtonpost.com/wp-dyn/content/article/2007/10/04/AR2007100400566_2.html


7.http://www.signonsandiego.com/uniontrib/20081017/news_1m17soledad1.html