Daly City California Coastal Erosion. Landslides, Erosion.... A Changing World скачать в хорошем качестве

Daly City California Coastal Erosion. Landslides, Erosion.... A Changing World

The stunning Daly City coast is one of the most actively eroding coastlines in the bustling San Francisco area which experienced a housing boom in the late 20th Century including along the Daly City seashore cliffs. The gigantic cliffs here is not as solid as it seems subject to coastal erosion and landslides from rain saturation, earthquakes and storm wave undercutting. Today we scramble and fly over the Daly City cliffs to explore the coastal erosion at the 3 Daly city beach access areas; 1) We start off at Avalon Canyon where there have been several massive cliff retreats and landslides over the last 30 years. (2) Then we review Muscle Rock landfill and the ongoing efforts to stop landfill from spilling into the Pacific Ocean and remember the houses lost. (3) Then we journey to Thornton beach park where a rail road, highway and houses have been claimed by coastal erosion. The original Highway 1 (Pacific Coast Highway, PCH) in Daly City, CA, ran much closer to the ocean's edge than it does today, but it was damaged and rendered unusable by a 1957 earthquake and landslides. Rates of erosion in these rocks can average up to two to three feet a year. That doesn’t mean two feet every year; it is an average rate of erosion over the past half century or so in which measurements have been made. Decades may pass with little erosion, relaxing concern about living at the edge of the sea. But in El Nino winters, coastal erosion can be rapid and severe. El Nino events bring a warming of ocean temperatures that can result in heavy rain in California (and drought elsewhere). In a major El Nino storm, especially if it occurs during a time of high tides, waves crash against the sandy Daly City cliffs. In the late 1800s little thought was given to the underlying geology when the Ocean Shore Railway Company started construction of its line down the coast. The railroad was built to connect San Francisco with the coastal resorts at El Granada, Miramar, and Half Moon Bay, and with the city of Santa Cruz. The line had been finished as far as Mussel Rock near Daly City when the 1906 earthquake caused the cliffs to fail, sending almost a mile of track and equipment into the sea. The railroad repaired the tracks and struggled for years to keep the trains rolling through soft, sandy soil that wouldn’t stay put. In 1920 the railroad stopped trying, victim of the high cost of maintaining a roadbed along the eroding cliffs. Undeterred by the railroad’s experience, in the 1930s the Department of Highways (now Caltrans) acquired the roadbed and constructed Cabrillo Highway (Highway 1). The road builders had trouble keeping soft sediment from flowing onto the pavement and the asphalt from sliding to the sea. They abandoned the attempt after the March 1957 Daly City magnitude 5.3 earthquake, which sent major sections of the road down the hill. The epicenters of both the 1906 and the 1957 earthquakes were on the San Andreas, not far from Mussel Rock near the Daly City border with Pacifica, where the San Andreas Fault heads to sea after its 600-mile journey through California from Mexico. At Mussel Rock the San Andreas Fault passes through a huge ongoing landslide, 9 million cubic yards of rock slowly moving seaward. The Mussel Rock landslide—the term in this case refers to a geographic feature rather than an event—extends out to sea for at least four miles and is thought to be the second-largest active landslide along the entire California coast. #coastalerosion #dalycity #changingworld