This is the second collapse to occur in the area recently. On August 22, a bluff at the foot of 11th Street partially collapsed, halting train traffic for hours.
Following that incident, geologist Pat Abbott explained that the bottom layers of the bluffs are made of strong, white stone. The material on the top is brittle sandstone.
"It’s so weak, it crumbles in my hands," Dr. Abbott said. “Ocean waves are on the bottom, people watering their plants soaking through the rock, seeping the strength out of it, all those things working to weaken an already weak rock, allow gravity to do its thing.”
Trains also run atop the cliffs, sending vibrations through the area throughout the day.
"Every little thing that weakens the rock speeds up the inevitable," Dr. Abbott said.