Sunday, February 28, 2010

Tsunami: Fail.

So I've been busy at school this past week and fallen a little behind on things I wanted to share on this blog. Here's one story...

At 6:00 Saturday morning, the siren started. Coming out of a dream that had incorporated this unexpected sound, I was confused. "Is this real?" I think I managed to mumble. As my brain woke up a bit more, I recalled the email we'd received from the university late the previous night: Earthquake in Chile, 8.8, tsunami advisory for 11:19 am... Ah. That's what it is. A tsunami alarm.

The siren was loud and long. They test the alarms at the beginning of each month, but I often don't hear it if I'm inside. I guess they don't run it as long in the tests as they do for the real thing, so it doesn't have time to get to full volume everywhere (since when it runs for minutes it cycles between high and low volume, I theorize that it projects in a certain direction and rotates around). But you'd have to be a very deep sleeper with earplugs in to miss this alarm. My three housemates and I each stumbled out of our rooms. The Ukrainian couple didn't know what was happening, so I filled them in.

We checked out the news. The tsunami advisory had by now been upgraded to a tsunami warning, which I believe indicates the highest degree of risk. It's hard to predict how big a tsunami will be when it hits various places--I don't even know what information they use to make the predictions. But they thought there was a possibility that this would be big. It was all over the news, even getting mentioned in national news. People were hitting up gas stations, buying fresh water and canned food (as if it were a hurricane, really), and heading for the hills. We were safely out of the reach of a tsunami, so we weren't worried.

Within an hour, the Housemate had gotten calls from both his brother and his mother on the mainland, since they'd heard about the tsunami warning on the news and wanted to make sure he was safely away from the beach. No one called me (I finally did get a call from my dad at 11:05, less than half an hour before it was supposed to hit). There was another alarm that sounded at 7:00. After briefly musing about grabbing his surfboard and heading down to the beach, to which I simply replied "No," the Housemate proposed that we go to Diamond Head to watch the tsunami. I thought it might be a bad idea because the authorities probably don't want people on the road during emergencies like this, but I was intrigued... As a physical oceanographer, wasn't it my duty to take this opportunity to witness a tsunami? I said I'd think about it.

Another alarm went of at 9:00. Some friends of the Ukrainian couple arrived to spend the day at our house, since their apartment was close enough to the shore to be evacuated. They brought tales of a Waikiki ghost town, everything closed, police waving people to turn around... I got a little more nervous about going out, but if we approached Diamond Head from the land side, there's no way they'd have closed all those roads down, and the volcano itself would of course be high ground and safe. The Housemate and I decided to go.

Around 10:40 we hopped in the car and drove off to Diamond Head. The roads weren't empty, but they were noticeably less crowded than would be usual for a Saturday. When we got there, we didn't drive through the tunnel to the crater (the path to the peak starts in the crater and zigzags its way up to the top); lots of people were already parked all along the road leading there and setting themselves up on a ridge, so we decided to do the same. We were settled and ready for the tsunami by 11:10. They were now predicting it would arrive some time around 11:35. So we sat there taking pictures of the crowd and the water, hoping for some nice contrasting "before" and "after" photos. We had a good view of Koko Head and the coast leading to it, including a region with a fairly shallow reef that we thought might be revealed as the water receded. We had a closer view of the water right by Diamond Head, but it was somewhat obscured in places by buildings and trees and wasn't so shallow. But it seemed like a relatively good spot. We waited.

I spouted nerdy physical oceanography stuff like "The tsunami would travel across the open ocean at approximately 200 m/s, assuming the ocean is 4000 m deep, which is a fair estimate of average open ocean depth." While a tsunami in the open ocean may not be very high, it is very long (couple hundred kilometers) and thus is associated with a great mass of water. Since it slows down as the water gets shallower (the speed of long gravity waves like tsunamis is simply sqrt(g*depth)), the water "piles up" as it gets towards shore, which is why it is high when it hits. Still, the wave heights may not be that impressive (though they can be enormous)--I think they were worried that ours might be 10 feet high. Waves on the North Shore can be 30ft+! But again, these are long waves, with periods of tens of minutes. The wave doesn't just wash up on shore and within seconds go back out. It keeps coming for minutes and minutes, pushing more and more water up onto the shore. I don't think any of us spectators were expecting some monstrous wave to leap up, knock down trees, and suck houses out to sea. That would have been pretty distressing, actually. But we were hoping to see some reef revealed or some beaches covered. We waited.

And we waited. People around us were calling friends who were watching the news. When is it going to hit? Did it hit the Big Island yet? After all the anticipation, the excitement, and the trepidation, there was nothing to see. I think the largest tsunami waves were 0.8 feet. A rise and fall of the water about equivalent to a tidal cycle was observed in bays, which tend to amplify the effects, but we weren't at a bay. One of our professors said that there was a huge mass of water measured by her instruments moving through the Ala Wai canal. So there was a tsunami, but there was no disaster. Nothing to get excited about. It was better, of course, that no one got hurt, and no shoreline or shoreline property was damaged. Still, after all the hype, we were disappointed. No fun pictures of the tsunami. Maybe next time.

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