Posteruptive thermoelastic deflation of intruded magma in Usu Volcano, Japan, 1992-2017

A talk on posteruptive deflation of lava domes in Usu Volcano, Japan, measured by Synthetic Aperture Radar given in the IPGP-ERI workshop.

Transcript

1. Posteruptive thermoelastic deflation of intruded magma in Usu Volcano, Japan, 1992–2017 Xiaowen Wang1,2 and Yosuke Aoki1 1 Earthquake Research Institute, The University of Tokyo 2 Now at Southwest Jiaotong University, Chengdu, China J. Geophys. Res. Solid Earth, 124, 335-357 doi:10.1029/2018JB016729 (2019) 2 October 2019 Workshop IPGP-ERI Paris, France
2. Inter-eruptive volcano deflation Nabro, Eritrea (Hamlyn et al., Prog. Earth Planet. Sci., 2018) Asama, Japan (Aoki et al., Geol. Soc. Lond. Spec. Publ., 2013) Kutcharo, Japan (Fujiwara et al., Earth Planet. Space, 2017; Yamasaki et al., JVGR, 2018)
3. Why studying volcano deflation? Potential mechanisms of volcano deflation ü Viscoelastic relaxation (Hamlyn et al., 2018; Yamasaki et al., 2018) ü Contraction of magma reservoir (e.g. Hamlyn et al., 2018) ü Cooling of emplaced lava (Wittmann et al., JGR Solid Earth, 2017) Temporal evolution of volcano deflation could carry various information such as rheology of intruded magma and host rock.
4. Toya caldera ü Usu volcano is located at the rim of Toya caldera which ejected >100 km3 of magma ~114,000 years ago. ü Eruption of Usu volcano in historical time: 1663: VEI=5 1769: VEI=4 1822: VEI=4 1853: VEI=4 1910: VEI=2 1944: VEI=2 1977: VEI=3 2000: VEI=2
5. Volcanic activity of Usu Volcano 1910 Activity time Eruptive Interval (yr) Location Eruption type Upheaval height (m) July ̶ Nov. 1910 57 North flank Phreatic 170 Dec. 1943 ̶ Sep. 1945 33 East flank Phreatomagmatic 280 Aug. 1977 ̶ Mar. 1982 32 Summit Phreatomagmatic 180 Mar. ̶ Aug. 2000 18 West flank Phreatomagmatic 80
6. A phreatomagmatic eruption in 2000 Showa Shinzan that emerged during the 1943-1945 eruption 280 m
7. Subsidence of the 1943 vent ü Persistent subsidence observed by leveling survey. ü Subsidence of 54 mm/yr (1965-1975) and 32 mm/yr (1975-1990) ü Current deformation? Spatial variation? Yokoyama & Seino (EPS, 2000)
8. SAR data processing JERS-1 ALOS-1 ALOS-2 Ascending Descending ü A total of 111 scenes from JERS-1 (1992-1998), ALOS (2006-2011), and ALOS-2 (2014-2017)． ü Time-series analysis from all possible interferograms (a total of 239 pairs).
9. LOS changes ü The 2000 eruption (Nishiyama) • Two subsidences • 38 mm/yr of LOS extension (mainly subsidence) between 2006 and 2011. • Negligible LOS changes between 2014 and 2018． ü The 1977-1982 eruption (summit) • LOS extension rate declines from 66 mm/yr (1992-1998) to 45 mm/yr (2006- 2011) and 43 mm/yr (2014-2017). ü The 1943-1945 eruption（Showa Shinzan）: • Stationary LOS extension rate of ~20 mm/yr Descending Ascending 2000 1977 1943
10. Decomposing (quasi-)EW and vertical velocities • EW contraction and subsidence. • The subsidence rate is higher than the contraction rate. 1977 1943 2000 1977 1943 NC KC ALOS-1 (2006-2011) ALOS-2 (2014-2017)
11. Modeling by thermal contraction V d Sea level Intruded magma body Surface Thermal diffusion Temperature Time elapse High Low V: source volume ; d: depth of the source; T: magma temperature (1200 K); a: thermal expansivity ( 2×10-5); k: thermal diffusivity; v: poisson ratio (0.25); u(x, t) = f (x, t, V, d, T, a, k, v) ü Assumed an intrusion of a spherical body (Furuya, 2004, 2005). Black: fixed Blue: model parameters
12. Optimum parameters ü The depth of the intruded magma is shallower than 400 m bsl． ü The apparent thermal expansivity is an order higher than the lab-derived value except for the 1943-1945 case. Longitude (°) Latitude (°) Depth ( m b.s.l) Volume (×106 m3) Thermal diffusivity (×10-5 m2/s) Misfit Data source 2000 site 140.8034 42.5541 213±19 6.67±0.21 8.21±1.01 2.78 ALOS-1 (NC) 140.8118 42.5563 100±13 2.05±0.13 8.06±1.20 2.02 ALOS-1 (KC) 1977 site 140.8353 42.5416 396±29 132.18±5.21 10.05±1.09 5.06 JERS+ALOS-1+ALOS-2 1943 site 140.8662 42.5426 92±12 49.51±2.12 1.65±0.22 1.03 JERS+ALOS-1+ALOS-2
13. Observation vs calculation 2000 vent 1977 vent 1943 vent ALOS- 1 JERS ALOS- 1 ALOS- 2 JERS ALOS- 1 ALOS- 2
14. The vent of the 1943-1945 eruption KC NC Vertical velocity map P1943 P1977 P2000
15. KC NC Vertical velocity map P1943 P1977 P2000 The vent of the 1977-1982 eruption
16. KC NC Vertical velocity map P1943 P1977 P2000 The vent of the 2000 eruption
17. Why is the apparent thermal diffusivity high? Hydrothermal convection effectively release heat from magma right after the intrusion? ü Lake Toya is right next to the volcano, providing groundwater. ü Frequent phreatomagmatic eruptions Question: Why is the apparent thermal diffusivity in the 1943 vent normal? Possible collaboration with IPGP: Reconstructing hydrothermal circulation beneath Usu volcano by numerical simulation.
18. Summary ü We measured ground deformation of Usu volcano by SAR images. ü Deformation is concentrated around lava domes that emerged during previous eruptions. ü The observed deformation is explained by thermal contraction of the intruded lava dome. ü The inferred apparent thermal diffusivity is larger than the lab-derived value especially right after the intrusion. ü Hydrothermal circulation effectively cools the intruded magma?
19. Earth Planets and Space Special Issue L-band Synthetic Aperture Radar: Current and future applications to Earth Sciences https://earth-planets-space.springeropen.com/lbsar Submission due: 31 December 2019 Guest Editors： Yosuke Aoki (Univ. Tokyo), Masato Furuya (Hokkaido Univ.), Francesco de Zan (DLR), Marie-Pierre Doin (ISTerre), Michael Eineder (DLR), Masato Ohki (JAXA), Mark Simons (Caltech), Tim Wright (Univ. Leeds)