USGS image of ropey pahoehoe from Kilauea, Hawaii
USGS image of glowing `a`a flow front advancing over pahoehoe on the coastal plain of Kilauea, Hawaii.
Contemporary Use of Computer Technology In the Study of Lava Flows
The work that I intend to carry out for my dissertation will focus on lava flows using data from Mount Etna, Sicilly. Two distinctive types of surface texture can develop on flowing lava, initially the rope like pahoehoe, then developing into clump-like ‘a’a.
USGS image of ropey pahoehoe from Kilauea, Hawaii |
The initial, pahoehoe stages of effusive eruption lavas are known to be higher in volatile content than further down flow, and to have an associated high vesicularity and vesicle number density. A key factor for creation of this surface texture is that the mean temperature is high enough to restrain crystal growth such that the microlite crystal content and crystal number density is lower. These combined properties of the lava create a low yield strength, allowing a laminar, thermally efficient, viscous sheet flow to occur even at relatively high effusion rates. Some ‘a’a develops early at the edges of the pahoehoe flow due to greater heat loss through radiative cooling from the turbulent substructure created at these margins. |
| Between 1.7 km and 1.9 km from the vent, the surface texture of the lava flow undergoes morphology changes from pahoehoe to ‘a’a although this is dictated by the lava properties, transport system and locality. Transition from pahoehoe is precipitated primarily by temperature drop which is accelerated by loss of volatiles, the release of which cause flow surface break up and more efficient radiative loss. With this change, vesicularity and vesicle number density decrease while microlite crystallinity and crystal number density increase. Crystallinity increase causes development of a large enough lava yield strength, thus preventing viscous flow, although all these components contribute to the viscosity-strain rate threshold being exceeded, causing the blocky surface of ‘a’a to form across the total width. |
USGS image of glowing `a`a flow front advancing over pahoehoe on the coastal plain of Kilauea, Hawaii. |
Contemporary methods of determining the temperature of flowing lava rely on inferred, indirect, temperature profiles. Certain crystals such as pyroxene and plagioclase, form in known temperature ranges and thus a relationship between crystal presence and lava temperature can be established. This technique is known as glass geothermometry. Although the use of the glass geothermometer has been shown to provide a reasonable estimate of relative quench temperatures, the use of indirect temperature measurement has been shown to be especially prone to errors. Direct sampling from live subaerial flows by manually suspending thermocouples on the lava is restrictive due to safety considerations and accuracy in specifying the location of the sampling point on the flow.