Lab 7; Due 11/23/10

Chaparral, Landslides and The Station Fire

California is unique in that it contains almost every ecosystem in the world (aside from tropical ecosystems). Coastal Southern California is made up almost entirely of the chaparral (or Mediterranean) ecosystem, a shrubland characterized by hot, dry summers, cool, wet winters and high levels of endemism. Most importantly for this report, the chaparral ecosystem is specially adapted to fire. For example, plants have unusually high levels of oil in their leaves, helping them to burn quickly. Though this may seem counter intuitive, it helps to ensure the survival of the plant by not allowing the fire to get hot enough to burn its roots. The plant (say, sagebrush) then epicormically resprouts—it resprouts from its roots.

Because of chaparral’s pleasant climate (think San Diego, Italy, South Africa) it has been a coveted place to live for centuries. Unfortunately, chaparral people are not as adapted to fire as plants are. When fire season rolls around in late summer, when those Santa Ana winds kick in, and when lightning strikes on oil-laden sagebrush, fires spread rapidly and people don’t know how to handle it. Not only do they not know how to handle the fires themselves, but they don’t know how to cope with the after effects. They can’t just epicormically resprout, so to speak.

The Station Fire (8/26/2009-10/16/2009) started in Angeles National Forest and burned over 150,000 acres in Los Angeles County. Though the fire was started by arson and was not a result of natural processes, it nevertheless took advantage of chaparral’s ideal fuel conditions and ripped through LA, causing millions of dollars in damage, thousands to evacuate their homes and even loss of life.

Station Fire burn scar from Dave's Landslide Blog
(image originally from NASA) 

Of particular interest to this report are the ways in which the Station Fire affected soil integrity. When chaparral burns, the aforementioned oil present in Mediterranean vegetation wafts into the air, settles, and forms a water impermeable layer on the surface of the soil. This, coupled with the lack of vegetation to hold the soil in place, can create a very undesirable outcome when it rains: landslides. Landslides were especially threatening after the Station Fire because of the hilly topography that was razed.

Debris flow scars in the greater Los Angeles area
from (http://www.eoearth.org/article/Landslide)

In 2010, storm warnings for southern California threatened flooding and mudslides. In February, unexpected heavy rainfall hit La Canada Flintridge, which had been burnt by the Station Fire a few months prior. 43 homes were damaged by a “niagra falls” of mud that came rolling down from the burnt hills surrounding the area. Luckily no one was injured; this is mostly due to the evacuation orders mandated by the cities of La Canada-Flintridge, Sierra Madre, La Crescenta and Acton. These evacuation sites are depicted in the map below. Arroyo Seco also experienced significant debris flow, but as it is not populated it did not need to be evacuated.

Example of 2/2010 mudslide in La Crescenta from (http://i.cdn.turner.com/cnn/2010/US/weather/02/10/california.mudslides/t1larg.mudslide.gi.jpg)

The USGS has installed instruments around the Station Fire burn scar to monitor debris flow in those areas. These instruments measure rainfall, soil moisture, flow stage and bed pore pressure and are intended to “advance the understanding of post-fire runoff, erosion, and debris-flow generation processes and to provide information from the burned area to the National Weather Service for warning decision-making” (http://landslides.usgs.gov/monitoring/). There are three such sites in Southern California, two in Dunsmore Canyon and one in Arroyo Seco, and are demarcated on the map below. Directly below is an example of soil moisture and rainfall data collection from http://landslides.usgs.gov/monitoring/.

Southern California’s Mediterranean/chaparral ecosystem is attractive to settlers because of its exceptionally mild climate characterized by hot, dry summers and cool, wet winters. However, chaparral is also very prone to fire; after an area burns it is also very prone to landslides. People are tying to adapt to these natural disasters, but evacuations are sometimes the only way in which to ensure safety. We are continually advancing our knowledge through monitoring sites and scientific data collection, and perhaps we will be better able to cope with fire (and landslides) in the future.

Bibliography

Landslide Hazards Program. Web. 20 Nov. 2010. (http://landslides.usgs.gov/).

"Landslide." Encyclopedia of Earth. Web. 20 Nov. 2010. (http://www.eoearth.org/article/Landslide).

"Latest Storm Prompts Evacuations for Station Fire Burn Areas | 89.3 KPCC." KPCC. Web. 20 Nov. 2010. (http://www.scpr.org/news/2010/02/19/storm-friday/).

"Malibu Surfside News: Rambla Pacifico Is Closed by Landslide." Malibu Surfside News. Web. 20 Nov. 2010. (http://malibusurfsidenews.com/blog/2010/02/rambla-pacifico-is-closed-by-landslide.html).

"Mudslides Occur in the Areas Affected by the 2009 Station Fire in Los Angeles." Dave's Landslide Blog. Web. 20 Nov. 2010. (http://daveslandslideblog.blogspot.com/2010/02/mudslides-occur-in-areas-affected-by.html).

"Mudslides Threaten California Hillside Communities After Station Fire | AHN." All Headline News. Web. 20 Nov. 2010. (http://www.allheadlinenews.com/articles/7016614039?

Mudslides%20Threaten%20California%20Hillside%20Communities%20After%20Station%20Fire).

"'Niagara' of Mud Hits Homes." Featured Articles From The Los Angeles Times. Web. 20 Nov. 2010. (http://articles.latimes.com/2010/feb/07/local/la-me-rain7-2010feb07).