Contemporary Use of Computer Technology In the Study of Lava Flows - Page 3

Images of lava flows can be analysed when the stored TIR files are downloaded to a PC or field laptop computer. Various image processing applications are available and in this case, Scion Image will be used. Image analysis can be performed by most processing software and although the surface plot provides a visual idea of where the peaks and troughs of temperature are across the all the image, more useful information may be obtained by a two dimensional section, which if taken a different transects, can indicate change in temperature along the image.

Scion Image uncalibrated temperature suface plot of earlier lava flow image, with section profiles

Improved presentation in graphics may be obtained by using a spreadsheet such as Microsoft Excel, and a comparison is shown here for the second of the two sections through the surface plot. The Excel image, even allowing for the larger size, is more manageable in terms of graphical presentation of data, as control is given for many things, such as the horizontal and vertical scales, tick marks and line style

However, the graphical output from the image processing and analysis software is based on a notional colour pallete that has been applied to the raw image data numbers. For this reason, these outputs do no not represent a true temperature reading. The raw data must be processed by specific conversion software that is correctly calibrated. This is being developed independently by a co worker at the Open University. When complete, it will complete the task of being able to determine and analyse temperatures of flowing lava, in the field.

Microsoft Excel chart of temperature profile of lava surface plot N.B. X axis is pixel number, Y axis is data number

With this TIR remote sensing technique for lava temperature monitoring, surface temperatures throughout the length of the flow can be obtained at much easier than using conventional methods. Lava core temperatures may also be inferred by taking TIR surface temperature readings and then obtaining glass geothermometry measurements of the same section once the lava has cooled. This calibration should provide a relationship between surface and core temperatures for future TIR measurements.

SURVEYING THE TERRAIN OF THE LAVA FLOW ENVIRONMENT

The landscape over which the lava is flowing plays an important part in the route that will be taken. In particular, the land profile can play an important part in the development of pahoehoe into ‘a’a. If a stable pahoehoe flow encounterd a steep gradient, the ensuing velocity increase and associated increase in strain rate could result in a transition. Likewise, the path that the flow takes is influenced by ground shape.

It is therefore important to have a satisfactory survey of the flank of the volcano over which the lava is flowing. Although, existing maps will exist, often the scale is insufficient to pick up local details. For this reason a survey may be required. Traditional methods of land surveying, still in use now, involve optical levels or theodolites. This manually recorded data is ultimately drawn by hand on film or paper. Increasingly though, this is a domain becoming dominated by computer technology. Hunter Husky Data Logger The intial land survey would be carried out with an electronic total station. This extends the function of the theodolite and allows rapid measurement of ground profiles. Data from the total station is downloaded into a data logger in the field. The survey data is later transfered into a p.c. where a CAD package such as AutoCAD® Land Development Desktop can produce various drawings of the terrain such as sections or plan views. Furthermore, the CAD software is able to carry out various assessments of the land, such as volume calculations. This has a relevance to lava activity, as good assessments of erupted product volumes may be obtained, using accurate survey data before and after eruptions.

Topcon Electronic Total Station DT-102

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Glossary (Return to text)

‘A’a – A lava texture much like rough clumps of ploughed soil, matt finish, from a Hawaiian name and now in general use.

CAD – Computer Aided Design/Drawing. This is a precise tool that has a wide range of uses, from centimetre accuracy of land surveys to sub-millimetre accuracy found in the semi-conductor circuit design.

Effusive – A non explosive form of eruption, whereby magma issues from a vent or fissure in a syrup like manner.

Electronic Total Station – This allows angles and distances to a given target to be measured. Usually the angle and distance will be displayed as a relative or absolute X, Y and Z ordinate set. This is often wrongly called an EDM. Although a total station does contain an electronic distance measurement device, this only represents part of the total station.

Microlite – An extremely small crystal not visible to the naked eye, representing the early frozen early stage in crystal nucleation and often found in frozen lavas.

Pahoehoe – Lava texture akin to coils of rope, glassy in sheen. Hawaiian name in general use.

Vesicle – cavity in lava caused by dissolved volatiles coming out of solution as pressure is reduced, such as happens at eruption.

Volatile – An element that in the high pressure and solubility of subsurface magma conditions remains dissolved, such as chlorine, fluorine or sulphur. The reduction in temperature that occurs as the magma reaches the surface, as lava, allows the gas to come out of solution.

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References

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Researched and produced by D.Haynes, February 2001

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