I
have recently started an Earth Art Fellowship with the School of Earth Sciences
at Bristol University, alongside a group of volcanologists working on what is
known – in shorthand – as the DisEqm project. DisEqm stands for Disequilibrium,
which I am told is a relatively new concept in volcanology and one which marks
a radical break with all previous laboratory models of volcanic eruptions which
were based on measurements taking during ‘equilibrium’ conditions, and are
therefore irrelevant to modelling conditions during an eruption when all of the
variables of temperature, pressure, viscosity etc are in constant flux:
disequilibrium.
The team at Bristol have spent the past 3 years building a high temperature, high pressure (HTHP) rheometer. A rheometer is a device that quantifies the viscosity of any given liquid by measuring the torque required to stir it. The challenge in this instance is to build an apparatus capable of stirring a tiny sample of magma that has been heated to temperatures as high as 1400˚C and at a pressure equivalent to that of magma 6km beneath the earth’s crust. What quickly becomes apparent from hearing about their progress is the extent of the artifice required to synthesise these conditions. In volcanological laboratories pressure and scale are inversely proportional: the higher the pressure you wish to emulate, the smaller your sample has to be – for the simple reason that large samples at high pressure are potentially extremely powerful explosives. In this case their sample is just 6cm long and a few millimetres wide. But to work at equivalent conditions to the earth’s core for example, your magma sample must be squashed into a space between two diamonds measuring just a few microns. Processes that occur in a subterranean layer more than 2000km thick are modelled in laboratories on the area of a single pixel of your screen.
In her
essay on the ‘Thermocultures of Geological Media’, Nicole Starosielski uses the
example of thermal image sensors composed of pure germanium doped with mercury
whose sensitivity to infrared frequencies is used in the geological remotely
sensing of minerals in the earth’s crust. To render these thermal images the
sensor itself must be “cooled to between −243.15 degrees and −196.15˚C… The
stabilisation of the thermal environment … in turn enables the remote detection
of temperature”. Although a measurement of temperature is not the experimental
goal, a similar dynamic is at work in the operation of the HTHP rheometer. To
measure the torque required to stir pressurised magma without simultaneously
melting your measuring apparatus requires several means of thermal control,
primarily through insulation and water-cooling, but also a physical
discontinuity between sample and instrument. The magma sample must be
pressurised and heated to 1400ºC, the electronics measuring the torque,
however, are required to remain at room temperature and atmospheric pressure.
So, while in a traditional rheometer the spindle stirring the liquid is the
same as that used to measure torque, here the sample must be stirred magnetically
to prevent the conduction of heat through the spindle.
Overheating is a common problem in technical
apparatuses. The central processing chip of a computer can reach temperatures
as high as 400˚C while performing CPU-intensive tasks. To mitigate these
extremes of temperature, which would otherwise crash software and permanently
damage the chip, a heatsink and fan are clamped against it using thermal paste to
ensure efficient transition of heat out of the silicon into the aluminium. Most
heatsinks used in consumer electronics are cast from pure aluminium, the
quintessential metal of contemporary technologies, and one with good thermal
conductivity. This thermal relationship between silicon and aluminium in electronic
circuitry is mirrored in the volcanology laboratory. The viscosity of magma
samples is governed by the proportion of silicon dioxide (SiO2) they
contain, and the crucibles in which these samples are melted are made of
Alumina (Al3O2). Computation extracts pure elements from
raw ores, refining rocks in order that they can micromanage electron flux, process
data, or record an image. But in exploiting their thermal and electrically
semi/conductive properties it inevitably imitates lithic processes. The
abstractions of computation are as reliant on the properties of the minerals
from which they are made as they are on the cultural manipulations performed to
those substances. The chemical properties of conductivity, photosensitivity, and
inscription play out geologically in earth processes just as they do technologically
in media processes.