Abstract

 
 
 
 On December 22, 2018 the south-western flank of Anak Krakatau collapsed into the sea, removing 93.8 × 106 m3 of subaerial lavas, and generated a tsunami. Synchronously with the collapse, a large volcanic plume of SO2 and ash (14–15 km in height) has formed, marking the onset of a paroxysmal eruption lasting from December 22, 2018 to January 06, 2019. From remote sensing analysis, we show that the eruption can be divided into three main phases. Phase I and II show both tephra and gas emissions while phase III is mostly degassing. The total amount of SO2 injected in the atmosphere is 173±52 kt, while the minimum bulk magma volume emplaced, estimated from a topographic reconstruction, is ?45 × 106 m3. This value compares well with a petrologic-based estimate of 56.4 × 106 m3, making the existence of external sulphur sources and sinks quite unlikely. The ice-rich ash plume formation shows that a strong sea-water/magma interaction was responsible for the phreatomagmatic activity throughout the eruption. However, we distinguish a first Vulcanian blast-derived eruption (lasting 40 min) just after the collapse having a Mass Eruption Rate (MER) of 9 × 105 kgs?1, followed by a sustained lower-intensity eruption resulting in ash emissions over hours (MER = 5 × 105 kgs?1). From December 23, daytime photos show typical Surtseyan activity.
 
 
 
Highlights
Anak Krakatau is a volcanic island located in the Sunda Strait (Indonesia), which emerged in 1927 on the rim of the submarine caldera that was formed during the 1883 eruption of Krakatau
Estimation of ash plume concentration and altitude are obtained from IR satellite-based data [Prata 1989a; Wen and Rose 1994]. These parameters are critical as they allow indirect assessment of the Mass Eruption Rates (MER) of tephra emitted at the source vent from empirical formulations [Sparks et al 1997; Mastin et al 2009] or statistical modelling [Gouhier et al 2019]
The volume of the subaerial volcanic cone of Anak Krakatau, built since 1927, has been estimated by Bani et al [2015] during a field campaign in 2014 to be ∼ 320 × 106 m3. This means that the minimum estimates of the bulk volume of tephra emplaced during the 22–29/12/2018 period (45 × 106 m3 during Phase I + II) represents the equivalent of ∼ 12 years of cone growth
Summary
Anak Krakatau is a volcanic island located in the Sunda Strait (Indonesia), which emerged in 1927 on the rim of the submarine caldera that was formed during the 1883 eruption of Krakatau. Bencana Geologi: https://magma.vsi.esdm.go.id) and photographs available on the web Estimation of ash plume concentration and altitude are obtained from IR satellite-based data [Prata 1989a; Wen and Rose 1994]. These parameters are critical as they allow indirect assessment of the Mass Eruption Rates (MER) of tephra emitted at the source vent from empirical formulations [Sparks et al 1997; Mastin et al 2009] or statistical modelling [Gouhier et al 2019]. The method might be further optimised in the future by better parameterising the drone survey and implementing GNSS GCPs, it provides a rough estimate of the new topography of the island less than 20 days after the collapse
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