Yes, parts of Los Angeles are sinking, a phenomenon known as land subsidence, where the ground slowly settles or drops below its previous elevation. While the entire region is not uniformly descending, specific coastal and inland areas are currently experiencing this downward movement. This geological process is a measurable form of vertical land motion that complicates the long-term stability of the metropolitan area. The sinking is driven by a combination of human activity and natural geological forces unique to the Los Angeles Basin.
Defining Land Subsidence in Los Angeles
Land subsidence is a localized geological process involving the gradual sinking of the Earth’s surface due to subsurface material movement. This is distinct from global sea-level rise, which refers to the increasing volume of ocean water. For Los Angeles, subsidence is a measurable fact, not a speculation, with rates that can vary significantly across the basin. It occurs when underground support, such as fluids or soft sediments, is removed or compacted, causing the overlying ground to collapse or settle. This phenomenon is a direct change in the land’s elevation, which effectively lowers the local sea-level baseline. The effects are particularly pronounced in areas built on unconsolidated or recently deposited sediments.
Primary Causes: Extraction and Tectonic Movement
The primary drivers of subsidence in the Los Angeles area can be separated into two distinct categories: rapid, human-induced extraction and slower, long-term tectonic movement. The most dramatic historical sinking events were a direct result of anthropogenic causes, specifically the removal of vast quantities of underground fluids. This includes the extensive historical extraction of oil and natural gas from the Los Angeles Basin’s petroleum reservoirs, a practice that removes structural support from the rock layers.
The most famous example is the Wilmington Oil Field, where rapid, early-20th-century oil extraction caused surface land to subside by over 9 meters (29 feet) in some spots between 1926 and 1968. Similarly, the historical withdrawal of groundwater from aquifers for municipal and agricultural use has also caused the compaction of compressible sediment layers. As water is pumped out, the pressure that holds the sediment grains apart decreases, leading to a permanent reduction in the rock volume and subsequent sinking of the land surface above.
Natural and geological forces also contribute to the long-term vertical movement of the land. The Los Angeles Basin is a complex tectonic setting, situated near the San Andreas Fault system, which drives slow, long-term uplift and subsidence along various fault lines. Furthermore, the natural compaction of relatively recent, unconsolidated coastal sediments adds to the sinking in low-lying areas, especially those built on reclaimed land. While natural forces operate over geological timescales, the extraction-related sinking in the past often occurred at a much faster rate, creating immediate and significant engineering challenges.
Localized Hotspots and Scientific Measurement
Subsidence is not uniform across the metropolitan area, instead concentrating in specific localized hotspots. Historically, the most significant sinking occurred in the harbor areas, with Wilmington, Terminal Island, and parts of Long Beach being severely affected due to intense oil extraction activities in the Wilmington Oil Field. This intense subsidence required extensive efforts to mitigate damage to the port infrastructure. Today, other areas, such as the Palos Verdes Peninsula, are experiencing slow downward motion, which is sometimes associated with slow-moving landslides and erosion.
Inland areas like the Santa Ana Basin also show measurable seasonal vertical movement related to fluctuating groundwater levels. Scientists use advanced satellite technology to track these subtle, ongoing changes across the entire region. The primary method is Interferometric Synthetic Aperture Radar (InSAR), which uses radar signals from orbiting satellites to measure ground displacement down to fractions of an inch per year. This technique is often combined with data from high-precision Global Positioning System (GPS) monitoring stations to create a detailed, three-dimensional picture of the land’s vertical motion.
Compounding Risks: Subsidence and Sea-Level Rise
The combination of land subsidence and global sea-level rise creates a significantly accelerated risk for low-lying coastal communities. When the land sinks and the sea rises, the effective rate of relative sea-level rise in that specific location is amplified. This means that coastal areas already experiencing subsidence will face flooding threats sooner and more severely than areas where the land is stable or rising. Studies have shown that this combined effect could increase local sea-level projections in parts of Los Angeles by up to 15 inches (40 centimeters) in the coming decades, magnifying flood risk.
This dual threat poses specific dangers to critical urban infrastructure and natural ecosystems. Sinking land stresses roads, bridges, pipelines, and wastewater systems, which are not designed to withstand differential movement. Coastal wetlands, which serve as natural buffers against storm surges, are also highly vulnerable, as they may be unable to migrate inland quickly enough to keep pace with the rapidly rising relative sea level. The long-term implications require ongoing monitoring and careful adaptation strategies to protect the densely populated and developed Los Angeles coastline.