EGU2020-10551, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-10551
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

InSAR Imaging of White Island from 2014 to 2020: Insights into the 2019 Phreatic Eruption

Yunmeng Cao1, Daniele Trippanera1, Xing Li1, Adriano Nobile1, Zhang Yunjun2, Luigi Passarelli1, Wenbin Xu3, and Sigurjón Jónsson1
Yunmeng Cao et al.
  • 1King Abdullah University of Science and technology (KAUST), Thuwal 23955, Saudi Arabia
  • 2Seismological Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 3School of Geoscience and Info-Physics, Central South University, Changsha, China

At 14:11 NZDT (01:11 UTC) on 9 December 2019, an explosive eruption (VEI=2) occurred on White/Whakaari Island in New Zealand’s northeast Bay of Plenty. The sudden eruption claimed 20 lives among the 47 tourists who were on the island at the time of the eruption. Several volcano-tectonic features overlap in the island such as a major caldera rim collapsing scarp to the west, a landslide, a crater lake and a large shallow hydrothermal system at the center, making complex the understanding of the eruption triggering factors. Here we use Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data from 3 different tracks (1 ascending and 2 descending) spanning the period of 2014-2020 to investigate the spatio-temporal surface deformation evolution of White Island in the years before the eruption. By analyzing the InSAR time-series displacements between the two eruptions of April 2016 and December 2019, at least 4 separate stages can be identified that possibly relate to different parts of the volcanic eruptive cycle:  1) During April 2016 - February 2018, the crater lake edge and the western sub-crater wall rapidly moved downslope at a rate of ~6 cm/yr, while the central sub-crater area uplifted at a rate of ~3 cm/yr; 2) From February 2018 to January 2019, both the western and the central sub-craters uplifted at a rate of ~5 cm/yr; 3) During  the following six months, from January 2019 to June 2019, the western sub-crater started moving downslope again at a rate of ~3 cm/yr, while the central sub-cater kept moving up at a rate of ~4 cm/yr; 4) And finally, during June 2019 - December 2019 (until the eruption), uplift occurred around the western sub-crater again at a similar rate as in the central sub-crater area (~ 4 cm/yr). Seismic records before the eruption show that approximately 500 volcanic earthquakes located at a depth of ~ 5 km occurred at the southwestern part of White Island on June 2019, that may point to a shallow level intrusion of new magma. This upcoming magma might then have pressurized the shallow hydrothermal system during the fourth-stage uplift. Modeling of the uplift during June 2019 to December 2019 indicates a shallow source located at only ~200 m below the surface in the vicinity of the crater lake, likely coinciding with the shallow hydrothermal system responsible for the final 2019 phreatic eruption.

How to cite: Cao, Y., Trippanera, D., Li, X., Nobile, A., Yunjun, Z., Passarelli, L., Xu, W., and Jónsson, S.: InSAR Imaging of White Island from 2014 to 2020: Insights into the 2019 Phreatic Eruption, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10551, https://doi.org/10.5194/egusphere-egu2020-10551, 2020

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Presentation version 3 – uploaded on 08 May 2020
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  • CC1: Questions and answers from the live chat during EGU2020, Michael Heap, 11 May 2020

    Q: Amazing observations. Have you done any geodetic modelling to try and constrain a deformation source process? 

    A: Thanks, a sill model for phase four show aa shallow source around 200m, at this stage, we mostly focus on the geodesy part. 

    Q: Whakaari has been very active in the last decade. One notable eruption/explosion, as indicated on your figure, was in April 2016. This event did not register in your displacement data. Why do you think the 2019 event could be seen in the displacement data when other eruptions/explosions could not?

    A: Before doing this, we also don't know whether can be seen or not.

    Q: Any idea on the depth and nature of the source of the deformation?

    A: The deformation source mostly due to the hydrothermal processes as a shallow depth (e.g., ~ 200m).

    Q: What was the reason for the subsidence at the beginning of 2019? Was there an increase in the amount of degassing? The first uplift did not lead to any eruption, so how well can we use these observations of uplift as a warning system?

    A: Yes, it is hard to use the uplift as a warning signal

    Q: Very interesting results! It could even be possible at phase 3 that there was dyking occurring, at least from first glance at the InSAR ground deformation map. Are there any additional datasets that can help constrain the modeling?

    A: Two more GPS stations are available on the Island, but both of them show small deformations (at least on the vertical direction).

    Q: Thank you! And do you know what caused the subsidence between 2019-2019.5?

    A: It is really hard to say, at this stage the crater level is also decreasing, which is mainly due to the steam condensing beneath the lake. 

    Q: Are these GPS stations located farther away from these main regions of ground deformation seen in the InSAR? It could be possible to decompose your InSAR displacement field into vertical and horizontal motion since you have both ascending and descending data. If the GPS stations are nearby to the deformation, it is possible that the majority of the displacement is actually horizontal motion.

    A: GPS stations are located at relatively stable area (Fig. 1), and the InSAR results is referred to one of the station, so, theoretically, these results have an absolute meaning.

Presentation version 2 – uploaded on 07 May 2020 , no comments
I changed the labels of Figure 2 a little bit.
Presentation version 1 – uploaded on 01 May 2020 , no comments