Open AccessA comparison of cooling‐limited and volume‐limited flow systems: Examples from channels in the P iton de la F ournaise A pril 2007 lava‐flow field
Author(s) -
Rhéty Maéva,
Harris Andrew,
Villeneuve Nicolas,
Gurioli Lucia,
Médard Etienne,
Chevrel Oryaëlle,
Bachélery Patrick
Publication year - 2017
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2017gc006839
Subject(s) - lava , geology , flow (mathematics) , volume (thermodynamics) , front (military) , rheology , open channel flow , petrology , volumetric flow rate , channelized , viscosity , volcano , mechanics , mineralogy , thermodynamics , geochemistry , physics , oceanography , telecommunications , computer science
Abstract Channel‐fed lava‐flow systems lack detailed thermal and textural studies through the boundary between channelized and dispersed flow, and out to the flow front. Here chemical, textural, and morphological analyses were made to define cooling and crystallization rates down the entire system, especially through the zone of dispersed flow. We compare two channel systems active during the 2007 eruption of Piton de la Fournaise, one of which was cooling limited and one of which as volume limited. In the cooling‐limited case, rapid changes in rheology occurred across the zone of dispersed flow, where viscosity increased from 1000 to 1600 Pa s over the last 100 m of the channel system. This was due to an increase in cooling rate from 7°C km −1 over the first 500 m of the system, to 42°C km −1 over the last 100 m, and an increase in microcryst content from 13% to 25%. In the volume‐limited case, the exponentially increasing segment of the down‐flow cooling and viscosity trend is absent. Instead, lava arriving at the flow front is still relatively hot (1161°C compared with a near‐vent temperature of 1167°C) and is thus of relatively low viscosity (1125 Pa s). In the volume‐limited case, because the channel was still in extension when supply to the system was cut, the zone of dispersed flow was extremely short. However, because lava behind the stalled flow front was still hot and fluid, breakouts from the static front resulted in a complex flow front morphology.