Lengths and hazards from channel-fed lava flows on Mauna Loa, Hawai‘i, determined from thermal and downslope modeling with FLOWGO

Abstract

Using the FLOWGO thermo-rheological model we have determined cooling-limited lengths of channelfed (i.e. 'a'ā) lava flows from Mauna Loa. We set up the program to run autonomously, starting lava flows from every 4th line and sample in a 30-m spatial-resolution SRTM DEM within regions corresponding to the NE and SW rift zones and the N flank of the volcano. We consider that each model run represents an effective effusion rate, which for an actual flow coincides with it reaching 90% of its total length. We ran the model at effective effusion rates ranging from 1 to 1,000 m 3 s 1 , and determined the cooling-limited channel length for each. Keeping in mind that most flows extend 1-2 km beyond the end of their well-developed channels and that our results are nonprobabilistic in that they give all potential vent sites an equal likelihood to erupt, lava coverage results include the following: SW rift zone flows threaten almost all of Mauna Loa's SW flanks, even at effective effusion rates as low as 50 m 3 s 1 (the average effective effusion rate for SW rift zone eruptions since 1843 is close to 400 m 3 s 1 ). N flank eruptions, although rare in the recent geologic record, have the potential to threaten much of the coastline S of Keauhou with effective effusion rates of 50-100 m 3 s 1 , and the coast near Anaeho'omalu if effective effusion rates are 400-500 m 3 s 1 (the 1859 'a'ā flow reached this coast with an effective effusion rate of $400 m 3 s 1 ). If the NE rift zone continues to be active only at elevations >2,500 m, in order for a channel-fed flow to reach Hilo the effective effusion rate needs to be !400 m 3 s 1 (the 1984 flow by comparison, had an effective effusion rate of 200 m 3 s 1 ). Hilo could be threatened by NE rift zone channel-fed flows with lower effective effusion rates but only if they issue from vents at $2,000 m or lower. Populated areas on Mauna Loa's SE flanks (e.g. Pāhala), could be threatened by SW rift zone eruptions with effective effusion rates of $100 m 3 s 1 .

Lava effusion rate definition and measurement: a review

“…Baloga et al 1995;Harris and Rowland 2001;Harris and Neri 2002;Jurado-Chichay and Rowland 1995;Keszthelyi and Self 1998;Keszthelyi et al 2000;Rowland et al 2003Rowland et al -2005. Effusion rates can also be obtained in this manner by integrating the vertical velocity profile through the entire flow thickness (Dragoni 1989;Dragoni et al 1986;Fink 1993;Oddone 1910;Tallarico and Dragoni 1999;Soule et al 2005).…”

“…Thus, effusion rate, velocity and volume are important input parameters into lava flow models and simulations, and/or have been the outputs of others (e.g. Costa and Macedonio 2005;Crisci et al 2003Crisci et al , 2004Favalli et al 2005;Glaze and Baloga 2001;Harris and Rowland 2001;Hikada et al 2005;Ishihara et al 1990; Keszthelyi and Self 1998;Keszthelyi et al 2000;Macedonio and Longo 1999;Rowland et al 2004Rowland et al , 2005Wadge et al 1994;Young and Wadge 1990). Finally, by representing material supplied from a deeper source, effusion rates allow constraint of mass flux out of the shallow feeder system, allowing assessment and/or modelling of the mass balance and dynamics of the effusing or extruding system, and of the source depth and conduit geometry (e.g.…”

“…They can also be used in predictive models designed to estimate the possible extent, and thus hazard posed by, advancing flows (e.g. Calvari and Pinkerton 1998;Costa and Macedonio 2005;Crisci et al 2003Crisci et al , 2004Favalli et al 2005;Ishihara et al 1990; Rowland et al 2005).…”

Hazard assessment at Mount Etna using a hybrid lava flow inundation model and satellite-based land classification

“…This may result from the fact that this was a compound flow field, which at times was fed by a complex tube system . FLOWGO is a model for channel-fed flow, where the development of tubes or well-insulated flow will mean that the lava will have the potential to travel further before reaching is cooling-limited extent at any given effusion rate (Harris and Rowland Rowland et al 2005). Fits between model simulations and field data for single, channel-fed units active within this eruption are, however, excellent if appropriate insulation conditions are used, and if single channel-fed flow units active within the flow field are considered (Harris et al 2007a).…”

“…To do this, we used the FLOWGO thermal-rheological input parameters defined for Etna by Harris et al (2007a), coupled with the effusion rate fitting adaptation applied to FLOWGO by Rowland et al (2005). This assumes an initial (at-vent) square channel, of width w and depth d (so that w = d), and iterates on channel depth to obtain the required effusion rate.…”