Quick Dips

Earthworks Extravaganza

Visitors to science centres later this year will have the opportunity to play with "volcanoes" and design "rivers" as part of a set of exhibits intended to let people get closer to some of the processes that have shaped the planet on which we live.

In the real world, most of these processes are difficult to see because they are too slow (like erosion and marine sedimentation), too fast (like earthquakes), too dangerous (like volcanic eruptions) or too inaccessible (like the source of Earth's magnetic field). Our new science curriculum asks teachers to make their students aware of these processes, but how can this be achieved?

The usual answer is take them on field trips and show them the results of these processes, and hope that they can imagine how it all happened. Another approach is to use analogies and simulations, everyday devices and processes that mimic at least to some degree the processes we can see or the processes that geologists infer from the evidence in rocks.

One example is volcanoes. Volcanic eruptions are driven by gases that are released from being dissolved in molten rock. An expensive simulation is the shaken champagne bottle -- when opened, the liquid is propelled for some distance by the gases, which suddenly are no longer dissolved in the liquid but become bubbles of gas in their own right (this is why you don't see the bubbles in champagne while the cork is still in it).

Immediately, two requirements for a volcano become obvious: the presence of magma -- the scientific name for molten rock that has gas dissolved in it, and that the containing vessel -- the rocks surrounding the "magma chamber" -- is sufficiently strong to contain this pressurised fluid. The fracturing of rocks, either by the movement of magma or other causes (which likely produce small earthquakes) is like decorking the bottle, and eruption occurs. Equally messy (but slightly cheaper) "eruptions" can be simulated from other beverages in tins. Hot beer, cold beer, hot cola, cold cola -- all have slightly different compositions and viscosities and thus erupt differently.

A rather more quantitative approach is to use a pump-up garden sprayer: the more you pump it up, the further the jet of spray goes when released. Thus, real magmas with less gas should not erupt as vigorously as those with more. With this simple piece of apparatus and a selection of liquids, it is readily demonstrated how the nature of the liquid -- its composition and viscosity -- as well as the amount of gas dissolved in it can be used to model volcanoes.

Not only this, but because the distance spurted by the sprayer decreases with time if the sprayer is left open and the gas pressure consequently reduces, you are led to the possibility that the violence of volcanic eruptions might decrease through a sequence. And geological field evidence often supports this: violent phreatomagmatic eruptions may be followed by gentler lava flows.

Such a volcano model is one of about thirty exhibits currently under construction for an exhibition scheduled to tour New Zealand's science centres later this year. Most exhibits will be interactive. Some, like the volcano described here and an "interactive geyser field" (based on the operation of a coffee percolator!), will lend themselves to experimentation. Others will enable participants to demonstrate for themselves how the tectonic plates into which geologists divide the Earth's surface move about, both now and in the past; how bits of New Zealand have moved relative to each other. They will be able to "map" a geothermal field on the basis of the conductivity of the "hot water" in the "rocks" below the exhibit. They will be able to design a miniature riverine landscape and then watch floods demolish it. Still others will enable particular properties of rocks, minerals and soils to be measured so that their suitability for particular purposes can be determined. Obvious examples are assessments of the response to vibration of various materials -- as could occur in earthquakes.

This exhibition, Earthworks, is being developed with a teachers' resource kit of activities to precede or follow viewing the exhibition. The package is targeted at forms one to four, but is intended to have a wide public appeal as well. Earthworks is a joint project between the Department of Earth Sciences and the Centre for Science, Mathematics and Technology Education Research at the University of Waikato and the EXSCITE Science-Technology Centre in Hamilton. Its development is being funded by the Ministry of Education.

Peter Hodder is a senior lecturer in earth science at Waikato.