| Update:
April 25, 2007 |
| Revisiting the VOG |
| By Pam Eastlick for THE DEEP on line |
Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.
Two years ago, I wrote an article in the Marianas Variety that generated a lot of comment. It was about our neighbor to the north, Anatahan. Anatahan is an active volcano (as are all the Northern Marianas Islands north of Saipan). Lately we’ve been getting a lot of haze over Guam and the Northern Marianas. The experts seem to be evenly divided over whether the haze is coming from Anatahan or mainland China and I suspect that the answer is that it’s coming from both of them. I think it’s time to revisit Anatahan and find out just what the danger is to Guam from the volcano in our back yard.
When I wrote the article in April 2005, Anatahan was actively erupting. It has since simmered down a great deal; the last recorded ash fall from Anatahan was in September 2005. It had a period of increased seismic activity in February and March of this year, but has since quieted down a bit. It continues to emit gas and steam and the winter storms that drive that gas and steam over Guam and the other Mariana Islands are still heading south. Should you worry about Anatahan and its effect on us? Enjoy the article (and some updated comments and information in parentheses).
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There’ve been some interesting rumors floating around lately about our neighbors to the north; specifically about the island of Anatahan. I’ve heard that Anatahan will definitely blow its top in a few weeks and when it does it will totally devastate Guam with 100 foot high waves, flowing lava, lava bombs and ash fall. People say that our government should immediately stop whatever they’re doing and turn all their attention toward preparing for and protecting us from this cataclysmic event. Anatahan, they say, will become another Krakatoa, the most destructive volcanic eruption in modern times. So, what are the facts about this potential catastrophe? |
| The island of Anatahan |
Well, first of all, it’s wrong to say that Anatahan will violently erupt in the next six months or so. (And obviously, from our vantage point two years later, it didn’t.) Volcanoes, like earthquakes are very unpredictable. Anatahan could go to sleep next week and not erupt again for 1,000 years. It’s also wrong to say that scientists thought Anatahan was extinct until it roared to life on 10 May 2003. All the islands of the Northern Marianas past Saipan (with the exception of Farallon de Medinilla) are dormant volcanoes and can erupt at any time. That’s what living in the ring of fire means.
Could Anatahan erupt catastrophically like Krakatoa? Sure, it could. In fact, Anatahan is very similar to Krakatoa before its cataclysmic eruption in August 1883. Both islands had been blown apart before in massive eruptions and Anatahan has the same large caldera that Krakatoa had. Anatahan is a small island two miles wide and six miles long, but its crater is four miles wide. Anatahan is mostly crater. (And the crater is bigger and deeper now than it was two years ago.) Krakatoa had a similar profile before 1883.
Anatahan could ‘go Krakatoa’ on us. So, what does that mean for Guam? Well, since the volcanoes are similar, it might be a thought to examine just what happened when Krakatoa erupted and how widespread the devastation was.
When Krakatoa blew up, the sound of the explosion was heard almost 4,000 miles away. It’s the loudest noise ever recorded. Here on Guam, we’ll know exactly when Anatahan blows (if it does), because we’ll hear it. So, if you hear something that sounds like an explosion or cannon or mortar fire, it just could be Anatahan.
But here’s the important part. Anatahan is 200 miles from Guam. The maximum reach of lava, pyroclastic bombs (big rocks thrown out of the crater with incredible speed) and pyroclastic flows (ground-hugging avalanches of hot ash, pumice, rock fragments, and volcanic gas that rush down the side of a volcano as fast as 60 mph) from the Krakatoa eruption was 50 miles. We don’t have to worry about any of these things here on Guam. We’re too far away.
Of course, you might be worried about that hundred foot tall wave generated by an Anatahan eruption that will destroy our whole island. Most of the people who died in the Krakatoa eruption died from the tsunami generated when the side of the volcano cracked open and seawater rushed into the magma chamber. The resulting steam is what actually blew the entire volcano apart.
That could happen at Anatahan too. The crater is big and the bottom of it is now around sea level according to the scientists who monitor the volcano. If Anatahan does have a cataclysmic eruption, it could very easily generate a gigantic tsunami.
But Guam is not vulnerable to tsunamis. A tsunami is a deep wave that must ‘run up’ an increasingly shallow sea floor. The sides of Guam drop off dramatically and almost vertically underwater. There is no place for a tsunami to gain height. A steam-generated wave could be quite large, but Anatahan is north-northeast of Guam. Any wave coming from that direction would hit the high, uninhabited cliffs that face the sea on all of northern Guam. I wouldn’t want to be on the beach up there if Anatahan blows, but you’d hear the explosion in plenty of time to head for higher ground.
There is, however, one consequence of a cataclysmic eruption of Anatahan that we just might have to deal with and that’s ash. When Krakatoa erupted, it put twelve cubic MILES of ash, dust and pumice into the air.
The ash and dust cloud completely covered the Sunda Straits and it was dark for around 20 hours after the eruption within a radius of 250 miles from the volcano. The darkness lasted more than 24 hours at places that were 130 miles away and over two days within a 50-mile radius of the volcano. In the immediate area, it was totally dark for three days.
So, if Anatahan does erupt violently, prepare for ash fall and lots of it. You’ll be shoveling and shaking ash off things for a long time. And prepare to get cold, because if it’s dark for a while, things cool off pretty fast. If Anatahan blows, it’s highly unlikely that you will be injured or die, but likely that you’ll be inconvenienced for a while.
Should the government stop what they’re doing and protect us from this menace? My question is; What are they going to do? Buy us all steel umbrellas? Maybe we should make Anatahan the site of our new dump and plug the vent with our trash. And then again, maybe not. Where ya gonna go when de volcano blow? I intend to ride it out right here. But I don’t think I’ll be visiting Saipan.
For more information, check out these web sites:
http://hvo.wr.usgs.gov/cnmi/
http://hvo.wr.usgs.gov/cnmi/update.html
www.drgeorgepc.com/Vocano1883Krakatoa.html
(Note: Vocano is not misspelled and this is a valid link)
