San Pedro Los Angeles Sunken City Geology

The Sunken City Geology
Overview
The Sunken City, as we know it today, came to be when a huge portion of Point Fermin, San Pedro, collapsed into the ocean, as a consequence of a massive landslide. This event, which occurred in 1929, left in its wake a trail of destruction. In essence, there are many kinds of landslides experienced in Southern California. These are identified by the U.S. Geological Survey (2017) as “shallow, rapid debris flows triggered by heavy rainfall, rock falls from steep slopes as a result of earthquakes, and sower moving slumps and earth flows on slopes that can fail under many different conditions.” It was the latter that was to blame in the case of the Sunken City.
History
In addition to being geologically complex, the area south of California has also been known to be tectonically active (the U.S. Geological Survey (2017). According to the Survey, it is this very complexity that controls not only where, but also when landslides occur, as was the case in San Pedro, Los Angeles. In 1929, a landslide that would end up being devastating on the public utilities front and with regard to reconfiguration of the landmass started on one of California’s prominent beach fronts – in the area of San Pedro. With the gradual slip of the land into the sea, emergency services managed to evacuate a significant number of people and save property, save for a few houses that were eventually swallowed up by the ocean. At the time, the landslide’s unexpected onset baffled geologists, and as a matter of fact, most were largely caught flatfooted. It was not until the landslide was underway that geological experts started investigating the area (Hyndman and Hyndman, 2016). However, as it has been observed elsewhere in this text, there may have been massive failure on the part of public officials due to the fact that prior to the establishment of the cliffside homes, no geological reports regarding the suitability of the area for human occupation were filed. The development of the site was done by George Peck, whose objective, according to Das and Sobhan (2016), was to establish an exclusive residential area offering its residents amazing views of the Pacific Ocean.
Today, the area is totally different from the way it looked pre-1929 – with the landscape having been totally reconfigured by the landslide. In recent times, the area has experiences several landslides, with the last one having been experienced 8 years ago (Bramlett, 2011).
Bentonite and Tectonic Activity
Sunken City’s bedrock comprises of sedimentary rock (layered), with one key feature of the layers, for purposes of this discussion, being bentonite. Bentonite weakens when it gets wet – with the weakness increasing with the level of wetness (Mutton, 2009). According to a Feasibility Report on Rancho Polos Verdes, Los Angeles County, CA, “bentonites are rich in the clay material montmorillonite, and become very weak when saturated by water” (U.S. Army Corps of Engineers, 2000, p. 3-1). As the report further point out, the landslide movement is in this case triggered by high levels of ground water which, in essence, “impact on the bentonite layers, as well as causing the saturated soils to become heavier and less stable, particularly along steep bluff areas” (U.S. Army Corps of Engineers, 2000, p. 3-1). In the case of the sunken city, the waves eroded the cliff’s underbelly, causing the layer to sip in water. Over time, it could no longer hold the weight and it at this point that the slide into the ocean begun. The slip into the ocean was, at first, not drastic – with approximately one foot of the ground going under water per day (Scholl, 2009). The decline was very slow during the very first days for residents to have a drastic ‘slipping’ experience. It is for this reason that officials were able to evacuate people while at the same time saving most of the bungalows before the main break occurred.
Landslides in California, according to the U.S. Geological Survey (2017), are not a rarity. The organization attributes this to tectonic activity. According to the survey, “in general, landslides are more common where slopes are steep and rocks are weak…” (U.S. Geological Survey 2017). In the recent past, the state’s infrastructure has borne the brunt of landslides, with electrical lines, pipelines, railroads, and even residential properties experiencing extensive damage.
Current Situation
Today, most of the area is fenced-off because of the obvious danger the cliffs and gaping holes pose to the general public (Brennan, 2015). It is important to note that although the area remains closed to the public, a few people still manage to sneak in to take pictures and experience the post-apocalyptic-like scene of what is left of the sunken city’s ruins. Most blocks of concrete are spray-painted – with many of the concrete blocks that served as building foundations being adorned with artistic patterns as well as paintings. Due to the various cliffs and dangerous ground-breaks, quite a number of fatalities have been reported, with most of those reporting injuries having fallen from the cliffs (Littlejohn, 2015).
According to Littlejohn (2015), pressure on officials to open up the area for public viewing continues to mount, with those in favor of such a move arguing that the ground has stabilized over time. They also argue that fencing has done little to keep curious members of the public at bay – with trespassing being more or less the order of the day. It is, however, unlikely that the area will be open for public access any time soon. This is more so the case given that the area still has loose rocks and steep cliffs. Further, it is important to note that the area’s land, by virtue of its hazardous geological composition presents a potential risk to any person who gains access.
Although some point out that there is little that could be done to restore the area, and perhaps ensure it is safe for public access (for viewing purposes, not for human inhabitation), I am of the opinion that stabilization measures could be adopted to bring down the risk of another land slide, or the gradual, albeit very slow slide which still occurs today, especially after a heavy downpour. Towards this endeavor, the authorities could make use of the City of Rancho Palos Verdes as a case study, with the area of focus being the Portuguese Bend Stabilization Project. The said project, according to U.S. Army Corps of Engineers (2000), consisted “of dewatering wells, drainage improvements, and grading of portions of the landslide.” The sunken city could adopt this particular plan, alongside the redistribution of the current landslide area mass. It was these very measures that contributed towards a significant reduction of the land slide movement in the Portuguese Bend Stabilization Project.
Conclusion
Due to the high probability of landslides in parts of California, the California Geological Survey is charged with the production of maps indicating locations that need evaluation or are at risk of land slide. In the case of The Sunken City, Hyndman and Hyndman (2016) point out that there was largely no geotechnical inspection conducted. Geotechnical inspections, in essence, “are commonly used in regards to soil solidity…” (Compaction & Soil Testing Services – CSTS, 2017). Failure to conduct geologic surveys at Fermin Port effectively led to the construction of homes on an unstable site.




References
Bramlett, J. (2011). Photos: San Pedro is Falling into the Ocean. Retrieved from http://laist.com/2011/11/22/san_pedro_is_falling_into_the_ocean.php#photo-1
Brennan, C. (2015). The Return of the Sunken City: Underwater Community of Exclusive LA Homes that Sunk into the Ocean 80 Years ago Set to Reopen to Curious Explorers. Retrieved from http://www.dailymail.co.uk/news/article-3079007/Sunken-City-abandoned-Los-Angeles-community-exclusive-coastal-bungalows-slid-ocean-foot-foot-reopen-public-post-apocalyptic-site-teenage-party-spot-decades-long-closure.html
Compaction & Soil Testing Services – CSTS. (2017). Geotechnical Inspections. Retrieved from http://www.comsoiltest.com.au/services/geotechnical-engineering/geotechnical-inspections/
Das, B.M. & Sobhan, K. (2016). Principles of Geotechnical Engineering (9th ed.). Cengage Learning.
Hyndman, D. & Hyndman, D. (2016). Natural Hazards and Disasters (2nd ed.). Mason, OH: Cengage Learning.
Littlejohn, D. (2015). Sunken City in San Pedro would be Open to the Public during the Day under New Proposal. Retrieved from http://www.dailybreeze.com/2015/05/11/sunken-city-in-san-pedro-would-be-open-to-the-public-during-the-day-under-new-proposal/
Mutton, K. (2009). Sunken Realms: A Complete Catalog of Underwater Ruins. Kempton, IL: Adventures Unlimited Press.
Scholl, S. (2009). Beaches and Parks in Southern California. Berkeley, CA: University of California Press
U.S. Geological Survey - USGS. (2017). Southern California – An Overview. Retrieved from https://pubs.usgs.gov/fs/2005/3107/pdf/FS-3107.pdf
U.S. Army Corps of Engineers. (2000). Rancho Palos Verdes Los Angeles County, Feasibility Report. Los Angeles, LA: Los Angeles District