"The Secrets of Supervolcanoes"

「スーパーボルケーノ 超巨大噴火の脅威」より抜粋

By Ilya N. Bindeman I. N. ビンデマン
English 日本語 日本語
Lurking deep below the surface in California and Wyoming are two hibernating volcanoes of almost unimaginable fury. Were they to go critical, they would blanket the western U.S. with many centimeters of ash in a matter of hours. Between them, they have done so at least four times in the past two million years. Similar supervolcanoes smolder underneath Indonesia and New Zealand. 米国西部,カリフォルニアとワイオミングの地面の下には想像を絶するような超巨大噴火を起こす2つのスーパーボルケーノ(巨大火山)が眠っている。そうした火山がひとたび眠りから覚めると,数日もかからずに米国西部のほぼ全域が厚さ数cm以上の灰の毛布で覆われることになる。
A supervolcano eruption packs the devastating force of a small asteroid colliding with the earth and occurs 10 times more often--making such an explosion one of the most dramatic natural catastrophes humanity should expect to undergo. Beyond causing immediate destruction from scalding ash flows, active supervolcanoes spew gases that severely disrupt global climate for years afterward. 超巨大噴火は小天体の地球衝突に匹敵するほど破壊的で,発生頻度はその10倍以上にもなる。高温の火砕流によって周辺地域の自然環境が瞬時に破壊されるだけでなく,大量に噴出する火山ガスのため,長期にわたって地球規模での気候変動が起こる。人類社会はいずれ,非常に破壊的なこの自然現象を経験することになるかもしれない。
Needless to say, researchers are eager to understand what causes these giants to erupt, how to predict when they might wreak havoc again, and exactly what challenges their aftermath might entail. Recent analysis of the microscopic crystals in ash deposits from old eruptions has pointed to some answers. These insights, along with improved technologies for monitoring potential disaster sites, are making scientists more confident that it will be possible to spot warning signs well before the next big one blows. Ongoing work hints, however, that supervolcano emissions could trigger alarming chemical reactions in the atmosphere, making the months following such an event more hazardous than previously suspected. いうまでもなくスーパーボルケーノは火山学の重要テーマだ。超巨大噴火はなぜ起こり,どんな困難な事態がもたらされるのか,いつ再び起きる可能性があって,どう予測するか。近年,こうした問いに対するいくつかの答えが,火山灰堆積物中の微小結晶の分析から得られ始めた。
Almost all volcano experts agree that those of us living on the earth today are exceedingly unlikely to experience an active supervolcano. Catastrophic eruptions tend to occur only once every few hundred thousand years. Yet the sheer size and global effects of such episodes have commanded scientific attention since the 1950s. 超巨大噴火の発生頻度は数十万年に一度。私たちが生きている間に起こる可能性は極めて低いと,ほとんどの専門家はみている。しかし,噴火の規模や地球環境への影響があまりに大きいことから,1950年代から研究が連綿と続いてきた。
One of geologists' first discoveries was the existence of enormous circular valleys--some 30 to 60 kilometers across and several kilometers deep--that looked remarkably similar to the bowl-shaped calderas located atop many of the planet's most well-known volcanoes. Calderas typically form when the chamber of molten rock, or magma, lying under a volcanic vent empties out, causing the ground above it to collapse. Noting that these calderalike valleys sit close to some of the earth's largest deposits of volcanic rocks laid down during a single event, those early investigators realized they were seeing the remnants of volcanoes hundreds or even thousands of times larger than the familiar Mount St. Helens in Washington State. From the extreme scale of the calderas and the estimated volume of erupted material, researchers knew that the magma chambers below them had to be similarly monstrous. 超巨大噴火の存在が知られるようになったのは,各地で巨大な丸く凹んだ地形が発見されたのが1つのきっかけだった。それは形としてはカルデラと似ていた。カルデラとは火山の山頂部でよく見られるお椀状の凹みだ。だが,規模はまったく違った。直径は30kmから60km,深さは数kmにも達した。
Because the thick continental crust and heat sources needed to create such massive magma chambers are rare, supervolcanoes themselves are also uncommon. In the past two million years, a minimum of 750 cubic kilometers of magma has exploded all at once in only four regions: Yellowstone National Park in Wyoming, Long Valley in California, Toba in Sumatra and Taupo in New Zealand. The search for similarly large eruptions continues in other areas of thick continental crust, including in western South America and far eastern Russia. 巨大マグマ溜まりを造るのに必要な2つの要素,厚い大陸地殻と熱源が揃うことはまれなので,超巨大噴火もそうは起こらない。一度に750km3以上のマグマを放出した噴火は過去200万年間でも世界で4地域だけだ。