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Stunning Vistas and Recent Storms

Posted by | December 28, 2010

Here’s a classic poem that’s dear to me, both for its manic intensity and its meaning in the natural world. It’s so short you can memorize it right now and always have it at your disposal when you consider news of storms and their destruction.

“Safe upon the solid rock the ugly houses stand: Come and see my shining palace built upon the sand!”

The poet was Edna St. Vincent Millay. Her lines always come to my mind when heavy rains ravage the West and homes, bridges and roads are swept away by mudflows and flash floods.

The poem seemed apt as California recently experienced torrential rains that triggered debris flows in canyons. Cascading down the steep hillsides, boulders, trees, mud and water flowed rapidly downhill, imperiling houses and those who lived in them.

As usual, there were reports from the people who had built houses exactly where we geologists would predict the debris flows would be the worst. They had traded safety for the stunning views of living in the steep canyons of southern California. In so doing, they had not built upon the rock, but on the sands of impermanence. When the land above their houses started to move, they instantly knew the significance of their choice.

“When you hear the boulders going ‘Bang, bang, bang,’ you know there’s going to be problems,” said canyon resident Steve Eighart to the Los Angeles Times.

Rapidly moving boulders are, indeed, your first clue you’re in deep trouble. That’s because boulders and other large objects like logs are at the front or “head” of the flow as it comes downhill. Behind that comes finer material like sand, and then a great deal of muddy water.

In some parts of southern California the authorities have built large depressions in the land called catch basins. They are meant to contain debris flows that reach them. Some basins have screens built into them to stop large objects like boulders while allowing the watery part of the flow to continue downhill.

Mike Colgan, who has lived in Orange County’s Silverado Canyon for 30 years, was impressed by recent events.

“This is only the second time I’ve seen this much debris flow, and it’s the first time I’ve seen it happen so quickly,” he told a reporter.

But Colgan also had a refreshing sense of personal accountability concerning his situation. “When you live up here, you should accept the responsibility of dealing with nature.”

The recent California flows were triggered by amazing rainstorms. By the end of the period, downtown Los Angeles was close to setting a record for the wettest December in 120 years, getting more than 7 inches of rain in seven days. For a dry part of the country, that’s a stupendous total. Actually, for pretty nearly anywhere it’s an impressive number!

As the storm moved inland it brought many feet of snow to higher elevations. It continued further, providing white holidays to people more than a thousand miles away from California.

The geologic factors that add to the dangers of debris flows in the West are steep slopes and loosened soils and rocks. Canyon walls are exceedingly steep, so it’s no surprise to geologists that they move downward when gravity overcomes a slope’s ability to hold itself up any longer. Bits of rock and soil then start heading downhill, and they can move as fast as a car on a highway.

Debris flow scars in the LA area
Old debris flow scars in the Los Angeles area (1968-9). Photo courtesy of the US Geological Survey.

Other factors also increase the chance of debris flows. Forest fires remove vegetation that helps hold a slope together. So fires in the West in the summer add to the possibilities of mudslides and debris flows in the winters to come. Human activities like cutting down brush and trees do the same.

Knowing where debris flow problems are likely, we could choose not to build on land that’s subject to frequent problems. That’s the logic of some zoning regulations. But people are often willing to risk the safety of their houses for the amazing views that canyons, bluffs and hillsides give them. They feel it’s better to have a “shining palace” that may not be permanent than a mundane house in a safer part of the world.

Perhaps there’s a poet born every minute.