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Article Dans Une Revue Bulletin of Volcanology Année : 2019

Investigating physical and thermal interactions between lava and trees: the case of Kīlauea’s July 1974 flow

Résumé

To examine whether there was any physical or thermal interaction between trees and lava when a lava flow inundates a forest, we studied the Kīlauea’s July 1974 lava flow. We mapped the location of ∼ 600 lava-trees and the lava type (pāhoehoe versus ‘a‘ā), and sampled an additional ten lava-trees for chemical and textural analysis to infer flow viscosity and dynamics. The emplacement event lasted 3.5 h and markers on the outer surface of the lava-trees allowed us to define initial high effusion rate and velocity (∼ 400 m3/s and 5–10 m/s) that then declined to 9 m3/s and 4 m/s during a waning phase. We find that lava passing through the forest underwent an initial cooling rate of 4 °C/km which increased to 10 °C/km late in the eruption. This is no different to cooling rates recorded at Kīlauea for tree-free cases. There thus appears to be no effect on cooling for this case. The lava-trees did, though, form a network of vertical cylinder obstacles and evidence for local diversion of flow lines are noticed. However, this varies with lava type, as almost no lava-trees form in ‘a‘ā. We find a relation between the percentage of ‘a‘ā and the number of lava-trees per hectare. The pāhoehoe–‘a‘ā transition for this flow occurs at a viscosity of 103 Pa s and this appears to be a threshold below which lava-trees can form so as to behave as a network of obstacles, and above which they cannot.
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Dates et versions

hal-02538123 , version 1 (26-11-2020)

Identifiants

Citer

Magdalena Oryaëlle Chevrel, Andrew Harris, Alexian Ajas, Jonas Biren, Lucia Gurioli, et al.. Investigating physical and thermal interactions between lava and trees: the case of Kīlauea’s July 1974 flow. Bulletin of Volcanology, 2019, 81 (6), ⟨10.1007/s00445-018-1263-8⟩. ⟨hal-02538123⟩
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