Abstract
Lava flow surface morphologies are like pages of a book. If we are able to read the writing of that book, we can understand its content, and learn, act, and react accordingly. In the same way, if we understand lava surface morphology, recognise how it formed and the hazard it poses while flowing, we can adopt actions to protect from lava flow invasion our villages, infrastructures and local population. The surface of lava is a function of intrinsic and extrinsic qualities, and their combination results in different shapes, sizes, and complexities, as well as in different hazards. Initial sheet flows spreading at high speed have great potential for devastating land, as happened in Hawaii in August 2018. However, their destructive potential significantly decreases with time and distance from the vent. Conversely, lava oozing from the far exit of lava tubes moves slowly but allows the tubes to expand, increasing gradually and slowly the potential hazard for invasion of more remote lands. In this paper, I present an overview of diverse lava flow surfaces, morphologies and structures in a framework of their generating eruptive parameters, in order to suggest preliminary but prompt hazard evaluations that could be applied during the initial phases of effusive volcanic crises at basaltic volcanoes worldwide.
Highlights
The final morphology of a solidified lava flow is the result of complex interactions between the lava and the environment in which it is emplaced
The analysis of lava flow morphology can help evaluate the possible hazard posed by active lava flows and lava flow fields, because each lava type forms in different phases of an eruption and in different conditions of discharge rate, lava rheology and topography
If we can measure the instantaneous effusion rate (IER) during an effusive eruption, we can apply the simple formula proposed by Walker [1971] that relates IER and maximum flow length, in order to estimate a priori the maximum distance that a single flow unit can reach from its vent, as has been done on Etna using Walker’s formula appropriately modified for Etna’s lava [Calvari and Pinkerton, 1998; Wright et al, 2001; Bonaccorso et al, 2015; Solana et al, 2017]
Summary
The final morphology of a solidified lava flow is the result of complex interactions between the lava and the environment in which it is emplaced. Most Hawaiian lavas initially erupt as pahoehoe, and may change to aa downstream as they flow away from the vent [Peterson and Tilling, 1980; Lipman and Banks, 1987; Cashman et al, 1999]. This transition is caused by cooling and by increase in viscosity and yield strength during flowage [Kilburn, 1981].
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