Satellite and Ground Remote Sensing Techniques to Trace the Hidden Growth of a Lava Flow Field: The 2014–2015 Effusive Eruption at Fogo Volcano (Cape Verde)

Abstract

Fogo volcano erupted in 2014-2015 producing an extensive lava flow field in the summit caldera that destroyed two villages, Portela and Bangaeira. The eruption started with powerful explosive activity, lava fountains, and a substantial ash column accompanying the opening of an eruptive fissure. Lava flows spreading from the base of the eruptive fissure produced three arterial lava flows. By a week after the start of the eruption, a master lava tube had already developed within the eruptive fissure and along the arterial flow. In this paper, we analyze the emplacement processes based on observations carried out directly on the lava flow field, remote sensing measurements carried out with a thermal camera, SO 2 fluxes, and satellite images, to unravel the key factors leading to the development of lava tubes. These were responsible for the rapid expansion of lava for thẽ 7.9 km length of the flow field, as well as the destruction of the Portela and Bangaeira villages. The key factors leading to the development of tubes were the low topography and the steady magma supply rate along the arterial lava flow. Comparing time-averaged discharge rates (TADR) obtained from satellite and Supply Rate (SR) derived from SO 2 flux data, we estimate the amount and timing of the lava flow field endogenous growth, with the aim of developing a tool that could be used for hazard assessment and risk mitigation at this and other volcanoes.

Understanding Lava Flow Morphologies and Structures for Hazard Assessment

“…At the beginning of many basaltic fissure eruptions, the discharge rate increases rapidly to a maximum value, then gradually drops to lower values as the eruption proceeds and the feeder dike empties [Wadge, 1981]. This behaviour has been observed and documented at several basaltic effusive eruptions and on different volcanoes, such as Etna and Stromboli (Italy), Fogo (Cape Verde), Holhuraun (Iceland), Piton de la Fournaise (La Réunion), Kilauea (Hawaii), [Hon et al, 1994;Calvari et al, 2005Calvari et al, , 2018Harris et al, 2005aHarris et al, , 2011Harris et al, , 2012Lodato et al, 2007;Spampinato et al, 2008aSpampinato et al, , 2008bGanci et al, 2012aCappello et al, 2016;Coppola et al, 2017;Patrick et al, 2017;Pedersen et al, 2017]. The general trend of declining discharge rate is overlapped by a local variability giving rise to pulses of the order of hours along the lava flow channel [Lautze et al, 2004;Bailey et al, 2005;Harris et al, 2005b], that re-FIGURE 2.…”

“…The lava flow field initially emplaced as thin pahoehoe lobes that gradually coalesced into larger sheet lobes [Guilbaud et al, 2005], an expansion similar to most pahoehoe lava flow fields observed today on Kilauea [Hon et al, 1994;Kauahikaua et al, 1998;Patrick et al, 2017]. At basaltic volcanoes like Etna and Stromboli (Italy), Kilauea (Hawaii), Piton de la Fournaise (La Réunion), Fogo (Cape Verde), or Holuhraun (Iceland), the general shape of a complex lava flow field is defined by a few arterial lava flows generally displaying aa texture, with its outline modified by secondary lava flows normally having a pahoehoe surface [Guest et al, 1987;Lopes, 1988, 1991;Calvari et al, 2005Calvari et al, , 2018Rhéty et al, 2017;Pedersen et al, 2017]. When lava tubes develop within complex lava flows, their hidden path is revealed by the distribution of skylights, ephemeral vents or breakouts, tumuli, shatter rings, or pressure ridges [Guest et al, 1980;Mattox et al, 1993;Calvari and Pinkerton, 1998;Kauahikaua et al, 1998Kauahikaua et al, , 2003Calvari et al, 1994Calvari et al, , 2018.…”

“…At basaltic volcanoes like Etna and Stromboli (Italy), Kilauea (Hawaii), Piton de la Fournaise (La Réunion), Fogo (Cape Verde), or Holuhraun (Iceland), the general shape of a complex lava flow field is defined by a few arterial lava flows generally displaying aa texture, with its outline modified by secondary lava flows normally having a pahoehoe surface [Guest et al, 1987;Lopes, 1988, 1991;Calvari et al, 2005Calvari et al, , 2018Rhéty et al, 2017;Pedersen et al, 2017]. When lava tubes develop within complex lava flows, their hidden path is revealed by the distribution of skylights, ephemeral vents or breakouts, tumuli, shatter rings, or pressure ridges [Guest et al, 1980;Mattox et al, 1993;Calvari and Pinkerton, 1998;Kauahikaua et al, 1998Kauahikaua et al, , 2003Calvari et al, 1994Calvari et al, , 2018. The formation of lava tubes significantly increases the hazard posed by an expanding lava flow because their insulating effect allows the flow to spread further down slope.…”

“…Effusive volcanic eruptions form either single lava flow units or compound lava flow fields, depending on the eruption duration: short-lived effusive pulses form single lava flows, also defined as volume-limited lava flows [Guest et al, 1987], whereas long-lasting eruptions promote the emplacement of complex lava flow fields Lopes 1988, 1991;Calvari and Pinkerton, 1998;Calvari et al, 2005Calvari et al, , 2010Calvari et al, , 2018Patrick et al, 2017;Pedersen et al, 2017]. A flow may generate major new lava streams by bifurcation, breaching and overflow of vents, channels, or tubes.…”

“…This transition is caused by cooling and by increase in viscosity and yield strength during flowage [Kilburn, 1981]. At Etna, Stromboli and Fogo volcanoes instead, aa lavas are the most common surface morphology among early lava flows, with pahoehoe becoming more widespread later in an eruption when effusion rate declines [Calvari et al, 1994[Calvari et al, , 2005[Calvari et al, , 2018Calvari and Pinkerton, 1998;Lodato et al, 2007]. Although pahoehoe and aa can be part of the same lava flow, they differ for temperature, viscosity, and vesicles shapes, with most active pahoehoe flows being less viscous and erupted at higher temperature than aa flows, and having vesicles normally as regular spheroids [Peterson and Tilling, 1980].…”