Anak Krakatau triggers volcanic freezer in the upper troposphere

Abstract

Volcanic activity occurring in tropical moist atmospheres can promote deep convection and trigger volcanic thunderstorms. these phenomena, however, are rarely observed to last continuously for more than a day and so insights into the dynamics, microphysics and electrification processes are limited. Here we present a multidisciplinary study on an extreme case, where volcanically-triggered deep convection lasted for six days. We show that this unprecedented event was caused and sustained by phreatomagmatic activity at Anak Krakatau volcano, Indonesia during 22-28 December 2018. Our modelling suggests an ice mass flow rate of ~5 × 10 6 kg/s for the initial explosive eruption associated with a flank collapse. Following the flank collapse, a deep convective cloud column formed over the volcano and acted as a 'volcanic freezer' containing ~3 × 10 9 kg of ice on average with maxima reaching ~10 10 kg. Our satellite analyses reveal that the convective anvil cloud, reaching 16-18 km above sea level, was ice-rich and ash-poor. cloud-top temperatures hovered around −80 °C and ice particles produced in the anvil were notably small (effective radii ~20 µm). our analyses indicate that vigorous updrafts (>50 m/s) and prodigious ice production explain the impressive number of lightning flashes (~100,000) recorded near the volcano from 22 to 28 December 2018. Our results, together with the unique dataset we have compiled, show that lightning flash rates were strongly correlated (R = 0.77) with satellite-derived plume heights for this event. Tropical thunderstorms can be triggered in a variety of ways. Common triggering mechanisms include solar heating, convergence of surface winds and the flow of wind over topography 1. A less studied mechanism is in the case of an erupting volcano where the input of heat at the surface initiates deep convection 2-4. Intense heating at ground surface and entrainment of moist air generates positive buoyancy 5 , which rapidly transports volcanic gases and ash particles up to the tropopause and beyond. Here we present the first detailed account of tropical deep convection triggered and sustained by magma-seawater interactions at an island volcano. Anak Krakatau ('Child of Krakatau') is an island volcano located in Indonesia's Sunda Strait (6 °06′07″S, 105 °25′23″E) between the islands of Java and Sumatra (Fig. 1). The volcano first appeared in January 1927 having formed in the caldera left behind by the famous cataclysmic eruption of Krakatau in 1883 6. On 22 December 2018, Anak Krakatau underwent a major explosive eruption after experiencing six months of intense Strombolian to Vulcanian activity. The eruption resulted in a flank collapse on the southwestern side of the volcano 7,8 , which generated a deadly tsunami that hit the coasts of Java and Sumatra at 21:27 LT (14:27 UTC) 9. The flank collapse marked the beginning of sustained phreatomagmatic activity at the volcano and led to the formation of a deep convective plume recorded by satellite for about six days. initial explosive event. We analy...

Correlation Between GNSS‐TEC and Eruption Magnitude Supports the Use of Ionospheric Sensing to Complement Volcanic Hazard Assessment

“…Considering the estimated propagation velocity of 1 km/s and the first arrival of the second perturbation (22:30, local time), the stronger gravity component observed in the second pulse can be attributed to the presence of a sustained plume in the atmosphere, rather than with the genesis of the tsunami. Indeed, the rise of the eruptive plume, constituted by a mixture of hot gas and particles, can displace the atmospheric medium inducing the propagation of gravity‐waves (De Angelis et al., 2011; Prata et al., 2020; Ripepe, De Angelis, Lacanna, & Voight, 2010).…”

Observations of lightning in relation to transitions in volcanic activity during the 3 June 2018 Fuego Eruption

“…Lightning data from the ENTLN was utilized to quantify lightning activity as sensed by ground-based networks. The ENTLN operates in a frequency range of 5 kHz to 10 MHz and detects rapid changes in the vertical electric field to pinpoint the location of IC and CG flashes 27,39 . In an inter-comparison between all global ground-based lightning location sensors, ENTLN provided the optimal performance in Guatemala when compared to the Lightning Imaging Sensor aboard the Tropical Rainfall Measurement Mission (TRMM) satellite 46,56,57 .…”

Downward-propagating eruption following vent unloading implies no direct magmatic trigger for the 2018 lateral collapse of Anak Krakatau

“…observations can constrain) and/or immediately followed by intense explosive activity (e.g., Perttu et al, 2020). The collapse cut the active conduit beneath sea level, resulting in Surtseyan eruptions that produced extensive ash deposits, rapidly buried the collapse scar, fed convective atmospheric plumes reaching 16-18 km (Prata et al, 2020), and involved a higher magma flux than anything recorded in recent decades (Gouhier and Paris, 2019). Here, we seek to determine the role of magmatic activity in the 2018 Anak Krakatau collapse, specifically addressing whether the intense accompanying volcanism was a driver or a consequence of edifice failure, by reconstructing magma ascent conditions spanning the syn-and post-collapse period.…”