VOLCANOES drop heavy hints before they erupt. For one thing they rumble and
start to bulge as molten rock rises up from below. You鈥檇 think then, with all
our seismographs and Earth-observing satellites, that pinpointing the time of an
eruption would be a cinch? 鈥淣ot necessarily鈥� is the resounding answer. The
eruption in the Congo last month was a grave reminder that these angry giants
can still surprise us.
In theory, researchers know what pre-eruption signals to look for
(see 快猫短视频, 12 January, p 28).
The trouble is watching one volcano won鈥檛 tell us
how another will behave. Every volcano has its own personality. That means we
don鈥檛 just need the right instruments, we need them in the right places,
clocking up data for a long enough time.
Mount Nyiragongo gave volcanologists trouble on all these counts. It had only
two seismographs and there was only one large eruption in 1977 to refer back to.
With this limited information, weeks before the eruption local volcanologists
could only tell Congolese officials that the volcano was restless. A false alarm
back in 1994 didn鈥檛 help. Instead of erupting, the lava kicked up a fuss but
never left the crater.
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The value of predictions will always be limited until we can be sure exactly
when a volcano is going to erupt, and preferably how much lava will spew out and
in what direction. If scientists had been able to predict with confidence what
they know with hindsight, officials might have taken more notice. If they had
been told that this year鈥檚 lava flood would be 10 times that of 1977, disgorging
200 million cubic metres of molten rock, and that it would probably devour a
third of the nearby city of Goma, they could have organised shelters and clean
water supplies. Property and lives could have been saved.
True, gathering more data doesn鈥檛 guarantee perfect predictions, but it will
make them better. Mount Etna, which like Nyiragongo leaks lava rather than
explosively ejecting it, is one of the most studied volcanoes in the world and,
partly because of that, it鈥檚 one of the most predictable. Last summer,
scientists warned a day ahead of time that the volcano would blow at 1.30 pm in
the afternoon. It was just three minutes late.
Even with a vague warning and inadequate preparations, the loss of human life
in Goma was thankfully small for such a huge natural disaster鈥攁bout 100
deaths. And the future for monitoring Nyiragongo looks good. Volcanologists
rushed to the Congo, and four new seismometers were on their way from donors in
France and the US. But what of the other 600 active volcanoes in the world, only
a dozen of which are constantly monitored? Many are near towns and cities.
Should we wait for them to 鈥渄o a Nyiragongo鈥� before acting? It doesn鈥檛 take vast
amounts of money or effort to set up seismographs on a volcano. And while our
forecasts will not improve immediately, it鈥檚 ridiculous to wait till disaster
strikes again before we make a start.
