Australian landscapes are ancient, the heady days when rift valleys tore Gondwana apart, and sea floor spreading propelled its fragments around the globe are long gone. It’s hard to imagine a Mt Nyrigongo popping up and obliterating Adelaide. And I do so miss her warmth, the twinkle in her magma and her sweet sulphurous perfume.
But the reality is that western Victoria is littered with volcanoes. It’s just the timing that’s out of kilter.
Ken Grimes, of the Hamilton Field Naturalists Club has written a very nice paper on the subject which you can find <HERE>.
In the Western District there are mainly three types of volcano, though combinations of these also occur. About half of the volcanoes are small steep-sided scoria cones built from frothy lava fragments thrown up by lava fountains. Most of the remainder are broader but flatter lava volcanoes formed from relatively gentle flows of lava welling out of a central crater. A group of about 40 maar cratersnear the coast formed from shallow steam-driven explosions which produced broad craters with low rims. These now often contain lakes.
These are the New Volcanics, they started about 5 million years ago. The most recent eruptions occurred about 5000 years ago. They seem to have occurred about every 5000 years so we may be due. According to Ken they erupt for a few weeks or months and never again, the next eruption being at a new site.
Melbourne University’s Professor Joyce anticipates that the next eruption would be “the sort of thing that would be interesting for tourists”. I’m sure it would, and Dr Lin Sutherland of the Australian Museum reassures us that
… no panic is needed. It probably would be a small discharge and a temporary nuisance, rather than the large eruptions we see in the Pacific ‘Rim of Fire’.
This assumes that it isn’t a Phreatic (15 points, more if you can get it on a double or triple word square) eruption. Boil one cubic meter of water and you have 1,600 cubic meters of steam. If magma comes into contact with ground water the result is an explosion. Such
explosions crush the overlying rocks and launch them into the air along with steam, water, ash and magmatic material. The materials usually travel straight up into the air and fall back to Earth to form the tephra deposits that surround the crater.
Thus producing a maar, these are usually a few hundred to a thousand meters in diameter and less than one hundred meters deep. Nothing to panic about.
Tourists do enjoy them but not until they’ve settled down a bit! My favorite is at Tower Hill near Port Fairy, incidentally this vicinity is high on the list for the next eruption.
It’s probably about 25,000 years since it went bang. It is now a very attractive game reserve, home to koalas, emus and kangaroos. Interestingly, you can’t take your dog there but during duck season you can take your gun.
So there you have it … photographic evidence of life on maars.
bobmcgee 