The lack of a tsunami warning system helped lead to the enormous loss of life when huge waves inundated coastal communities along the Indian Ocean last month. People in the northwestern United States are already familiar with such a system, which alerts residents and visitors in case of an evacuation order.

While regular tsunami warning drills take place along this part of the Pacific coast, authorities in one Oregon town wanted to make sure people would pay attention to them. So the Cannon Beach fire board decided to use the sound of a cow. Each month, the 1,600 residents of Cannon Beach – and, each summer, its thousands of beach-going visitors – hear a mooing sound broadcast from loudspeakers mounted on power poles around town.

“Test, test, test. This is a test,” begins the recording. Then the townspeople hear the baying of a cow, followed by a reminder that – in the event of a real tsunami emergency -- a wailing siren will replace the mooing cow.

The drills were inspired by memories of a 1964 tsunami spawned by a 9.2-magnitude earthquake in Alaska. It was the second-largest earthquake ever measured, even stronger than last month’s 9.0-magnitude quake in the Indian Ocean. The waves that rolled southward from the quake's epicenter were only three meters high when they crashed into Cannon Beach and obliterated the town's highway bridge. Miraculously, only four people died.

Since then, two smaller earthquakes and a mysterious sonic boom have provoked actual evacuations. But geologists are focused on what is expected to occur some time in the future in what is called the Cascadia Subduction Zone. In this area – located along a 1,300-kilometer fault line in the Pacific Ocean, not far off the Oregon coast  -- two of the great tectonic plates that form the earth's crust crunch together. 

“It builds up stress and builds up stress until it lets go in a humongous earthquake,” says Oregon geologist James Roddey, who says such a quake occurs once every few hundred years. “California [to the south] will never experience an earthquake the size that we someday will get in the Pacific Northwest,” he says, “because the plates in California are parallel to each other. Here, we've got one plate trying to dive under the other plate. But they get hung up, locked together, and at some point it lets go. So we're definitely within this window for another one of these great magnitude-nine subduction zone earthquakes and massive tsunamis to happen in the Pacific Northwest.”

It would be the same kind of catastrophic event that just roiled South Asia. Beneath the sea, the earth's crust rumbles -- not for a few seconds as in many inland earthquakes -- but for up to five devastating minutes, triggering wave after monster wave. “It will create a tsunami that could be nine, 12, 15 meters high when it hits the Pacific Northwest coast,” says Mr. Roddey.

Cover of a children's book on tsunamis from the Western States Seismic Policy Council - illustration by Joe Hunt

No wonder that Cannon Beach and other Oregon towns sound their tsunami alerts, and that Cannon Beach Elementary School holds earthquake and tsunami drills three times a year. After ducking under their desks in the earthquake exercise, everyone inside the school quickly evacuates in mock anticipation of tsunami waves.

“We meet out on our playground,” says head teacher Suzy Roehr. “Our third-grade and second-grade students go first across our field and through a gate. And then our fourth grade pairs up with our first grade, and our fifth grade pairs up with our kindergarten class, so there are older students to help the younger students. We have a bridge that we then have to cross, and then we go up a hill area that gets us up to the fifteen-meter level and higher. So we do take it very seriously, and we know that if we feel movement, or hear our town sirens going, that we're going to evacuate.”

Similar drills take place from northern California to Canada's British Columbia. And along beaches and roads, detailed tsunami information signs carry a stark, attention-getting graphic. It shows a human figure, scrambling up a hill as four massive waves close in.