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 channel-fed (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 m3 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 non-probabilistic 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 m3 s−1 (the average effective effusion rate for SW rift zone eruptions since 1843 is close to 400 m3 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 m3 s−1, and the coast near Anaeho‘omalu if effective effusion rates are 400–500 m3 s−1 (the 1859 ‘a‘ā flow reached this coast with an effective effusion rate of ∼400 m3 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 m3 s−1 (the 1984 flow by comparison, had an effective effusion rate of 200 m3 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 m3 s−1.