Textural, thermal, and topographic constraints on lava flow system structure: the December 2010 eruption of Piton de la Fournaise

Understanding Lava Flow Morphologies and Structures for Hazard Assessment

“…Pre-existing topography affects the form of the channel network in different ways, depending if we are dealing with aa or pahoehoe flows. At Mauna Loa, Dietterich and Cashman [2014] found that steeper slopes correspond to higher braiding indices on pahoehoe flows, whereas Soldati et al [2018] at Piton de la Fournaise described structures of the aa channel network varying with distance from vent rather than with time, with single channels forming on steeper slopes and braided channels on shallower slopes. Soldati et al [2018] observed that changes in the architecture of the aa flow are reversible because the flow can switch back and forth between single and braided channel configurations multiple times during its emplacement.…”

“…At Mauna Loa, Dietterich and Cashman [2014] found that steeper slopes correspond to higher braiding indices on pahoehoe flows, whereas Soldati et al [2018] at Piton de la Fournaise described structures of the aa channel network varying with distance from vent rather than with time, with single channels forming on steeper slopes and braided channels on shallower slopes. Soldati et al [2018] observed that changes in the architecture of the aa flow are reversible because the flow can switch back and forth between single and braided channel configurations multiple times during its emplacement. In addition, Soldati et al [2018] recognise the importance of flow rate on lava flow structures, with lava flows characterized by low effusion rates more prone to braiding compared to high effusion rate flows on any given slope.…”

“…flect more frequent pulses occurring at the main vent [James et al, 2007]. High effusion rate has been related to a greater crystal content of the lava (up to 70%), whereas it apparently has no effect on lava porosity, which is uniformly decreasing with distance from the vent [Soldati et al, 2018]. An important parameter affecting lava flow emplacement speed is the roughness of the topographic surface on which the flow is spreading, with greater roughness increasing flow brecciation and favouring the change from pahoehoe to aa [Rumpf et al, 2018].…”

“…Lava flows are non-Newtonian or Bingham fluids, and as soon as a lava flow stabilises, it develops a channel zone. Thus the channel is a zone of flowing lava contained between static levées Lipman and Banks 1987;Kilburn and Guest 1993;Soldati et al, 2018]. Channel formation results from an increase in flow surface velocity in the axial zone of a flow, with the velocity gradient between the rapidly moving central area and the stagnating margins becoming greater with time and eventually abrupt, and is marked by an initial channel generally much wider than in the stable channel zone [Lipman and Banks, 1987].…”

“…Lipman and Banks [1987] have classically described the architecture of channelfed lava flow systems, recognising four zones down a channel-fed lava flow: (1) a proximal, stable channel zone where levées are well-developed and mostly static ( Figure 6); (2) a medial, transitional channel zone, where the flow is channelized and bounded by incipient rubble levées still deformable; (3) a distal dispersed flow zone, where there are no levées and the lava is moving across its entire width; and (4) the flow front or flow toe, where the system is still spreading and expanding. The channel propagates downslope along the transitional and dispersed flow zones, where there are no levées present and the flow core is covered by breccia all the way to the flow front [Soldati et al, 2018]. This change confined a progressively greater volume of faster moving lava to a smaller channel cross section in an upstream direction, until the surface of the central area became more incandescent and finally consisted dominantly of fluid lava [Lipman and Banks, 1987].…”