Seismic Precursors to the Whakaari 2019 Phreatic Eruption detected in Five Other Volcanoes

Volcanic eruptions that occur without warning can be deadly in touristic and populated areas. Even with real-time geophysical monitoring, forecasting sudden eruptions is difficult because their precursors are hard to recognize and can vary between volcanoes. Here, we describe a general seismic precursor signal for gas-driven eruptions, identified through correlation analysis of 18 well-recorded eruptions in New Zealand, Alaska and Kamchatka. We show that the displacement seismic amplitude ratio, a ratio between high and medium frequency volcanic tremor, has a characteristic rise in the days prior to eruptions that likely indicates formation of a hydrothermal seal that enables rapid pressurization. Applying this model to the fatal 2019 eruption at Whakaari (New Zealand), we identify pressurization in the week before the eruption, and cascading seal failure in the 16 hours prior to the explosion. This method for identifying and proving generalizable eruption precursors can help improve short term forecasting systems.

Interpretation of Recent Unrest Events (Bradyseism) at Campi Flegrei, Napoli (Italy): Comparison of Models Based on Cyclical Hydrothermal Events versus Shallow Magmatic Intrusive Events

Several recent models that have been put forth to explain bradyseism at Campi Flegrei (CF), Italy, are discussed. Data obtained during long-term monitoring of the CF volcanic district has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically; these data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-102 yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (103-104 yr) magmatic system enclosed by an impermeable carapace (A layer). Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when the systems are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation that seals cracks and serves to isolate the two reservoirs. Faults and fractures promote outgassing and reduce the vertical uplift rate depending on fluid pressure gradients and spatial and temporal variations in the permeability field. The miniuplift episodes also show “bradyseism signatures” and are well explained in the context of the short timescale process.

How to Predict Earthquakes by Using Simple and Reliable Method? Peru, Chile, Italy, Greece, New Zealand, Andaman and Nicobar Islands, India

This paper intended to highlight the simple, quick and reliable method to detect impending earthquake�s location. Volcanic eruption precursors are originated only around the volcanos, like that the onshore earthquake precursors are originated only from earthquake epicenter zones. Epicenter zones are earthquake zones, a little variation of fault zone, it comprises movable tectonic plates. Due to the orbital motion of the earth, centrifugal force generated, this centrifugal force is the major driving force of tectonic plates. The position of the orbital motion of the earth generated seasonal variations/atmospheric weather anomalies as onshore earthquake precursors and earthquakes, year after year repeating at same places. The generation process of seasonal weather anomalies is the part of generation process of earthquakes at epicenter zones. Both seasonal weather anomalies and seismic anomalies are not continued all through the year at same places. When earth comes to particular position, tectonic plates of particular epicenter zones are set to more active and becomes unstable epicenter zones, causes identifiable, observable, recordable and testable onshore earthquake precursors 1-15 days prior to earthquakes occur.

Insights into the 9 December 2019 eruption of Whakaari/White Island from analysis of TROPOMI SO2 imagery

Small, phreatic explosions from volcanic hydrothermal systems pose a substantial proximal hazard on volcanoes, which can be popular tourist sites, creating casualty risks in case of eruption. Volcano monitoring of gas emissions provides insights into when explosions are likely to happen and unravel processes driving eruptions. Here, we report SO2 flux and plume height data retrieved from TROPOMI satellite imagery before, during, and after the 9 December 2019 eruption of Whakaari/White Island volcano, New Zealand, which resulted in 22 fatalities and numerous injuries. We show that SO2 was detected without explosive activity on separate days before and after the explosion, and that fluxes increased from 10 to 45 kg/s ~40 min before the explosion itself. High temporal resolution gas monitoring from space can provide key insights into magmatic degassing processes globally, aiding understanding of eruption precursors and complementing ground-based monitoring.

Investigation of the pre-eruptive processes of the 2014/15 Holuhraun eruption based on extracted volcanic tremor signals

<p>During volcanic unrest, multiple subsurface processes can happen simultaneously and may lead to an eruption. The analysis of seismic records in an unrest period before an eruption reveals information about the pre-eruptive processes and might be able to provide hints for a possible future eruption.</p><p>The 2014–2015 Holuhraun eruption was the largest one in Iceland in 230 years. It was extensively monitored and studied in a variety of multidisciplinary research approaches. Intense seismicity and ground deformation were interpreted as magma propagation from Bárðarbunga volcano 48 km laterally at ∼6 km depth over two weeks before an eruption started at Holuhraun. Different processes including vertical and lateral magma migration, dike propagation, caldera subsidence, and subglacial eruptions happened in this period and some models linking these processes are suggested. In the two-week interval preceding the eruption, there is still no clear connection between the observed tremor and pre-eruptive processes. Both the tremor source location and tremor generation process are not well understood yet. While cauldrons as a sign of subglacial eruptions were identified on the glacier surface from aerial photos, these cauldrons might have been formed earlier and there is hence an uncertainty of a few days. A tremor location might help to constrain these dates. However, the simultaneous occurrence of intense seismicity and tremor hinders the study and location of tremor. Here, we use a recent volcanic tremor extraction algorithm (Zali et al., 2020) and extract pre-eruptive tremor signals in order to better locate them using the Seismic Amplitude Ratio Analysis (SARA) method. Furthermore, the occurrence of the tremor could open new insights into ascending magma and fluid migration as well as the timing and duration of the subglacial eruptions.</p><p>We also observed short-lived tremors before the eruptions on August 29 and 31, which could be considered as eruption precursors. The primary investigation on the extracted tremor signals is promising while further analysis is on-going.</p>

Testing the application of Permutation Entropy to characterize the precursory phase of volcanic eruptions

<p>Permutation Entropy (PE) has been suggested to be a promising tool for the prediction of volcanic eruptions. It is a robust yet simple tool to quantify the complexity of time series. The application has been used in the biomedical and econophysics fields and recently was adopted to find precursors of volcano eruptions and to identify tremor episodes. However, in the different eruption cases, the temporal variation of PE was found behaving in different ways. For example, a gradual drop of PE was observed few days prior to the 1996 Gjalp eruption while it remained high prior to the 2012 Copahua eruption. Our final aim is to quantify what features in the PE can be interpreted as eruption precursors and whether this is applicable to different eruptions from the same or different volcanoes. In calculating the PE, the determination of two key inputs, namely the delay time and the embedding dimension, is crucial as PE depends strongly on those parameters. Here we present several tests on different types of synthetic signals with different signal to noise ratios to determine the most suitable input parameters. We found that when the delay time is much shorter than or equal to the dominant period of the signal, the value of PE will be strongly influenced by the noise. Thus, the value of the delay time should be chosen in between. Furthermore, the embedding dimension should not be smaller than 5 to be able to identify the characteristic of the underlying signal. Finally, we show the application of this method to the seismic data during the dike formation and the effusive eruption at Holuhraun, Iceland, in 2014-2015.</p>