In response to your cover article “Lords of the Rings”, I make these observations.

If Montecito installs canyon ring nets to catch debris flows, and people do not evacuate because they have ring nets for protection, then those ring nets have created a new threat to public safety.

Ring nets are an engineering solution to a natural event. All engineering solutions have limits — they are built to withstand something, such as a debris flow of a particular size or force. Whatever those limits are, natural events can exceed them. Also, stuff happens. The unusual, the unlucky, the unforeseen, the unforeseeable.

I know way too many examples, as I’ve spent years as a geophysicist with a focus on keeping communities safe during natural disasters. I’ve got special respect for debris flows. For sheer unstoppable deadliness, they’re second only to explosive volcanic eruptions (think Mt. St. Helens, not Kilauea).

At scientific meetings after Japan’s 2011 tsunami, I heard stories that continue to haunt me. Japan’s coastal communities face ongoing tsunami threat, and many have engineered solutions such as tsunami walls, which are designed to divert tsunamis up to a particular size. In 2011, many people knew a tsunami was coming but didn’t move to higher ground because evacuation is a hassle and the wall had stopped other tsunamis. So they stayed in harm’s way and thousands died. Their tsunami wall was not designed to protect them from the event that happened that day. Different disaster, different culture, important lessons for us here.


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