| There are few natural events which speak of man's insignificance quite as clearly as a volcano. We don't hear about most of them, but at any given moment, there's a volcano erupting somewhere around the world. Often these displays of might are simply spectacular like Killawog on the island of Hawaii. Occasionally they're catastrophic. There are 600 live volcanoes on earth, five of which are in New Zealand.
Unless you knew, you wouldn't recognize Lake Taupo as a volcano. It's actually a collapsed volcanic crater, and below the water the volcano bides its time.
As peaceful as it looks, Taupo has a history of violence. It has erupted 28 times in the last 25,000 years. The last was 1,800 years ago, an event known as the Taupo Eruption which bears the distinction of being the most violent volcanic event the world has seen in the last 5,000 years.
Taupo is a scientific challenge unlike most volcanoes in New Zealand. It hasn't gone off during recorded history. That means there's just no written information about eruptions. In order to guess its behavior in the future, scientists need to know about its behavior in the past and that requires some detective work.
The past record of the volcano makes it quite clear that it will erupt again almost certainly. The question is when and where and what it will do when it erupts again. In detecting the mystery of Taupo, Colin Wilson is a far-seeing scientist. He's one of a team of researchers from the institute of geological and nuclear sciences that has been studying the volcano for more than a decade.
By looking at different layers that we find in the deposits, we can recognize the products of individual eruptions, also we can trace these layers between different localities and measure their thickness and plot these on a map to get an idea of how big each eruption was. By measuring sizes of fragments carried to this locality and then comparing this to other sights, we can calculate roughly how high eruption column was, hence how powerful the eruption was.
Using these very simple techniques, in the most mundane locations, Colin is building a profile of the volcano's past. For instance, he has already discovered that the Taupo eruption devastated 20,000 square kilometers in 10 minutes.
This is a flow deposit erupted around 3,500 years ago. It was probably put into place here at about three or four hundred degrees centrigrade. You can tell this from the way in which wood fragments in the deposit have turned completely to charcoal. The structure and the distribution of this particular deposit suggest it came through here at around 200 kilometers an hour.
Lake Taupo itself has a starring role in this detective story that not only is it evidence of what has gone before, it also holds clues to what might happen next. The Lake works like a giant spirit level which can tell us if the ground is moving. And it is. The most dramatic movement is at the northern end where the land is actually sinking at fairly rapid rate of seven or eight millimeters a year.
Peter Otway knows this because he has been monitoring the level of the lake since 1979. Every three months, Peter measures the water level at 21 fixed points around the lake. By comparing the average readings at each place and filtering out normal water movements, he can calculate any changes in land levels. There's nothing high-tech about this work, but it's accurate.
It's a slumbering giant. At the moment we can see it breathing and really this is what we're monitoring breathing movements of the volcanco. Every now and then, it'll gives a wee twitch.
Bradley Scott is also involved in the surveillance of Taupo. But his focus is away beneath the surface.
Well here we're looking at the vertical component from the seismometer, and this is just the background motion. Increase in aperture is where I tapped it to confirm its working.
There are 15 permanent seismic stations in the Taupo volcanic zone. Portable seismographs like this one are used for more detailed research. Seismic activity is one of the prime early warning signals of volcanic hazard.
If magma is going to erupt, it will start to move within the earth's crust and force its way up to migrate to the surface. In other words, it has to open conduits and break rocks, and the rock breaking process generates earthquakes, so recording earthquakes in the volcanic terrain and finding background levels allow us to determine what the volcano is doing.
The Taupo region experiences up to 250 small earthquakes every year. These are normal background activities which in no way threatens daily life. While Bradley and Peter keep an eye on Taupo's present behavior, Colin reconstructs its past. They all hope its future will become clearer.
Right now, their profile is of a wildly erratic volcano that can be mild, or violent prolific in its eruptions, or passive for centuries. No one knows when Taupo will erupt again. They just know that it will one day.
没有什么能像火山爆发一样, 清楚地体现出人类的渺小了。我们对火山知道得不多, 但地球上的火山活动是非常频繁的。这些自然力量的展示常常是非常特别的, 如夏威夷岛上的基拉沃格火山。有时, 它们是灾难性的.地球上有600座活火山, 其中有5座在新西兰。
除非你事先知道,否则你不会把陶波湖看成火山。它实际上是倒坍的火山口, 在湖水下面, 火山蓄势待发。
看上去很平静, 其实陶波有着不同凡响的历史.在过去的25000年里, 它爆发过28次, 最后一次是在1800年前。而这一次是过去5000年里, 人类所见的最剧烈的一次爆发。
陶波是对科学的一个挑战, 不像大多数的新西兰火山, 在人类记载的历史上, 它没有爆发过,也就是说没有火山喷发的文字信息。为了猜测未来的火山爆发情况, 科学家们必须了解它的过去, 这就需要做一些调查工作。
关于火山的记载清楚地表明, 它将再次爆发, 问题是什么时候, 在什么地方爆发。再次爆发时,它将怎样？在对陶波火山的调查工作中, 科林·威尔逊是一位前瞻型的科学家,也是来自核地理研究所的研究小组成员之一，这个研究所研究火山问题已有十多年了。
通过观察地层中的不同层面, 我们能辨认出每次爆发后的产物, 我们也调查了不同地点的地层, 测量它们的厚度, 并在地图上标出相应的位置, 这样就能知道每次爆发有多剧烈了。通过测量被带到这一地点的碎片, 然后把它和其它地点的进行比较, 我们能粗略地算出喷发有多高, 有多强烈。
运用这些简单的技术, 在这些不起眼的地方, 科林正致力于重现这座火山的过去。他已经发现陶波火山的喷发在十分钟内就洗劫了2万平方公里的地区。
这是一个大约3500年前喷发的岩浆流层, 它流到这里时有300或400℃。这一点, 你可以从地层中完全炭化了的木质碎片看出。这些沉积的分布和结构表明, 它是以每小时200公里的速度到达这里的。
陶波湖在这次调查中的重要作用, 不仅在于它为以前发生的一切提供了证据, 而且还为将来要发生的一切提供了线索。湖本身就像一个大的水准仪, 它能告诉我们大地是否在运动。最显著的运动发生在湖的北部。在那里，地层以每年7或8毫米的惊人速度在下沉。
彼得·奥特韦知道这些, 因为他从1979年开始, 就一直对湖进行监测。每3个月, 彼得都会测量湖面上21个固定点的水位。通过比较每个位置的平均读数，去掉正常的水位变动, 他就能计算出湖底层的任何变化。这项工作不涉及高科技,但它是精确的。
我们在看测震表上的竖直部分, 这只是背景移动。我拍打的地方孔隙在增加, 这就证明它在工作。
如果岩浆即将喷发, 它会先在地壳内流动, 然后向上流向地球表面。换言之, 它必须打开一个通道, 击碎岩石, 而岩石的碎裂过程就产生了地震。因此，记录火山地带的地震和找出基础地层水平位置就使得我们能够确认火山的活动。
每年，陶波地区要经历多达250次的小地震, 这算是正常的地理活动, 对日常生活毫无影响。在布拉德利和彼得关注陶波现在的活动的同时, 科林在重建它的过去，他们都希望它的未来能变得更明朗。
现在, 它是无规律可循的火山，在喷发时可能很温和, 也可能很剧烈, 甚至也可能沉睡数个世纪。没有人知道陶波何时再次喷发, 只知道总有那么一天会再次喷发。