Abstract
The 2014-2015 eruption at Holuhraun has produced more than 1.5 km 3 of basaltic magma and can be considered one of the major effusive events of the last two centuries in the world. During this eruption the MIROVA system (a volcanic hot-spot detection system based on MODIS middle infrared – MIR - data) has been used to detect and locate the active portions of the lava flow(s), and to measure the heat radiated by the growing lava field. According to these data the eruption was characterized by a slow decay of the radiant power, accompanied by a change in the lava transport mechanism that shifted from open channels, at the beginning of the eruption, to lava tubes, during the last months of activity. Despite the evident evolution of lava transport mechanism, we found that the overall decreasing trend of the thermal flux was mainly controlled by the exponential decline of lava discharge rates, while the increasing insulation of the flow field had a strong impact in transporting efficiently the lava at the distal flow front(s). Our results suggest the apparent time averaged lava discharge rates ( TADR ), derived from satellite thermal data, may fluctuate around the real effusion rate at the vent, especially in the case of large lava flows emplacing in nearly flat conditions. The magnitude and frequency of these fluctuations are mainly controlled by the emplacement dynamic, (i.e. occurrence of distinct major flow units), while the transition from channel- to tube-fed lava transport mechanism play only a minor role (±30%) in the retrieval of TADR using MIR data . When the TADR values are integrated to calculate erupted lava volumes, the effects of pulsating emplacement dynamic become smoothed and the eruptive trend become more clear. We suggest that during the Holuhraun ’s eruption, as well as during many other effusive eruptions, the MIR-derived radiant flux essentially mimic the overall trend of lava discharge rates, with only a minor influence due to the emplacement style and evolving eruptive conditions. From a monitoring and operational perspective, MIROVA demonstrates to be a very valuable tool to follow and, possibly, forecast the evolution of on-going effusive eruption.
Highlights
On August 29th 2014, one of the largest effusive erup− tion of the last 3 centuries took place along the Eastern Volcanic Zone (EVZ) of Iceland (Figure 1), about 45 km north−east of Bárðarbunga volcanic system [Gudmun− sson et al, 2014]
In this paper we present time−averaged lava discharge rates and volumes, derived by using MIROVA system, and we compare the results with field and independent mea− surements collected during and after the Holuhraun erup− tion
We show that the overall trend of thermal emission was related to the combined effect of two over imposed patterns: (i) a main expo− nential decay of the effusion rate trend, governed by the source processes and (ii) a secondary pulsating pattern related to the emplacement dynamic of the flow field
Summary
On August 29th 2014, one of the largest effusive erup− tion of the last 3 centuries took place along the Eastern Volcanic Zone (EVZ) of Iceland (Figure 1), about 45 km north−east of Bárðarbunga volcanic system [Gudmun− sson et al, 2014]. The prohibitive environmental conditions that might characterize these latitudes made field observations at the eruptive site very hard, especially on a continuous basis and for several months during the winter time. In these conditions, space−based thermal data have been extremely useful since they allowed a safe detection, location and quantification of the radiant flux produced by the effu− sive activity. Since the beginning of the eruption the main tasks of satellite thermal data were: (i) to provide information about the location of active lava flow areas and front, (ii) to give an estimation of lava discharge rates and erupted volumes and (iii) to identify the ongoing effusive trend (steady, waning or waxing). The comparison reveals the role of changing em− placement style in the lava discharge rates calculation and outlines the contribution of MIROVA in safely tracking this large effusive eruptions from space
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