Quick Dips

Erebus Puzzle

The earthquakes and lava explosions of the Antarctic volcano Mt Erebus have puzzled scientists for decades, but Victoria University geologist Dr Ray Dibble believes he has some answers.

Many small earthquakes are recorded on the mountain each day, and the largest of these are associated with explosions of molten lava. Geologists have been trying to determine whether the earthquakes precede the explosions or whether the explosions cause the tremors.

The data has been difficult to interpret, even with computer enhancement. The earthquake waves were found to be travelling much faster than previously estimated, and yet were being recorded as if the earthquakes occurred 1.5 seconds after the explosions were timed on TV.

Dibble believes the delay is due to the presence of bubbling magma --  the earthquake waves are being slowed as they travel through the molten rock. Moreover, the waves are travelling steeply downwards from the explosions before being bent back up to the surface. The bubbling can be seen from the crater rim or from within the snow-covered crater itself.

"You can see the lava surface begin to swell, and then it takes one to 15 seconds for the bubble to burst," says Dibble.

"When the bubble bursts, it can cause a shock wave which some say has been strong enough to knock them off their feet, although I suspect they might have fallen over partly because of the fright they got."

Dibble has spent the last ten years monitoring the volcano, often sleeping on the crater rim to watch the slow movement of the lava lakes and to wait for explosions.