InSAR Imaging of Aleutian Volcanoes: Monitoring a volcanic arc from space

Zhong Lu1 & Dan Dzursin2 1. Southern Methodist University 2. U.S. Geological Survey

Acknowledgements: • Contributions by many colleagues. • SAR images from ESA, NASA/ASF, JAXA, CSA, and DLR. Outline • Volcano deformation • Aleutian volcanoes • What we have learned about Aleutian volcanoes from InSAR imaging Volcano Deformation: Why?

1. Many volcanic eruptions are preceded by pronounced ground deformation in response to increasing pressure from magma chambers or to the upward intrusion of magma.

2. Surface deformation patterns can provide important insights into the structure, plumbing, and state of restless volcanoes.

3. Surface deformation might be the first sign of increasing levels of volcanic activity, preceding swarms of earthquakes or other precursors that signal impending intrusions or eruptions.

4. Surface deformation provides a critical element on understanding how a volcano work. InSAR Applied to Volcanoes • InSAR can identify and monitor surface deformation at quiescent and active volcanoes. • InSAR can derive models of magma migration consistent with surface deformation preceding, accompanying, and following eruptions to constrain the nature of deformation sources (e.g., subsurface magma accumulation, hydrothermal-system depressurization resulting from cooling or volatile escape). • InSAR can monitor and characterize volcanic processes such as -dome growth and map the extent of eruptive products (lava and pyroclastic flows and ash deposits) from SAR backscattering and coherence imagery during an eruption, an important diagnostic of the eruption process. Similar methods can be used during or after an eruption to determine the locations of lahars or landslides. • InSAR can map localized deformation associated with volcanic flows that can persist for decades to understand physical property of volcanic flows, guide ground-based geodetic benchmarks, and help avoid misinterpretations caused by unrecognized deformation sources. Deformation Modeling

• Estimate source characteristics from InSAR deformation data

forward model InSAR image design

~7 km G s = d

source displacement s parameters (vector)

inverse model inv s = G d ~50 - 200 km

Lu et al., JGR, 2003 Deformation Source Models

Simple Source Models in Elastic Half-Space • Spherical Point Source • Prolate Ellipsoid • Sill or Dike for volcanoes • Penny-shaped Sill • Pipe • Distributed sources u = ƒ(model parameters, material properties, Complicating Effects …, ) • Non-uniform Elastic Structure • Topography • Viscoelasticity • Poroelasticity • Homogeneous • Thermoelasticity • Elastic • Complex Geometry • Half-space • Influence of hydrothermal fluid Aleutian Volcanoes • ~8% of the world’s active volcanoes. • ~75% of the historically active volcanoes in U.S. • ~2 eruptions per year in the arc. • Aleutian volcanoes span the entire spectrum in – eruptive style – eruption size/volume – magma composition • Although the rate of eruptive activity is very high, deformation monitoring using GPS has been possible at only a few Aleutian volcanoes, owing to the remote location, hostile climate, difficult logistics, and high cost of field operations. InSAR Imaging of Aleutian Volcanoes  ERS-1, ERS-2, JERS-1, Radarsat-1, Envisat, ALOS, TerraSAR-X imagery of 1990s-2010  25,000 InSAR images plus modeling & analysis

Becharof Discontinuity

• Lu and Dzurisin, Springer, 2014 Deformation of Aleutian Volcanoes is Common

 Historically active volcanoes: 52  No evidence of surface deformation:13  No useful information (decorrelation or poor spatial resolution): 8  Surficial deformation: 7  Magma intrusion: 21 + Strandline Lake  Deep-source deflation: 3  Erupted volcanoes: 17 (1992-2010)

 In contrast to Cascades volcanic arc:  Large volcanic centers: 12  Deformed volcanoes: 4  Eruption: 1

Surprising fact: so much of the volcanic activity in the Aleutians—a region noted for snow and ice cover, locally dense tundra vegetation, rapid surface change, and notoriously bad weather—is amenable to study with InSAR Deformation Styles are Diverse  Spatial variations in deformation patterns among various volcanoes  Temporal changes in deformation behavior at individual volcanoes.  Reflects the fact that Aleutian volcanoes span a broad range of eruptive styles, sizes, magma compositions, and tectonic settings.  Differing deformation patterns suggest differences in magma plumbing systems.

Unimak Island Fisher

Westdahl Shishaldin

5 km

Inflation of a few cm/year Subsidence of 1-2 cm/year No significant deformation (Lu et al., 2000, 2003, 2004) (Lu et al., 2007) (Lu et al., 2003; Moran et al., 2006) Open-conduit Volcanoes can Erupt Without Deforming  Most frequently erupted volcanoes: erupt without deforming appreciably  Seismicity extends to greater depths beneath individual volcanoes  A large proportion of earthquakes deeper than about 10 km are low-frequency events indicative of fluids  Stratovolcanoes with symmetric cones  Several interpretations:  no significant pre-eruptive and co-eruptive deformation was associated an eruption => Magma accumulation/transfer occur relatively quickly  Short-lived pre-eruptive inflation was balanced by co-eruptive deflation and no net displacement could be observed  The magma source is very shallow and magma strength is small so that deformation could only occur over the region of lost coherence.  Call for InSAR images with shorter time separations (a few days) and continuous GPS measurements near the summit to capture localized deformation if it exists.

 A long list of volcanoes outside the Aleutian arc that fit into this category: Aracar, , , Irrupuntuncu, , , Nevado del Chillan, , , , , , and Villarica in the ; Dempo and Merapi in west Sunda; Bezymianny, Kliuchevskoi, and Sheveluch in Kamchatka, … Insignificant co-eruptive deformation at frequently erupted stratovolcanoes

92-day ALOS interferogram 1993-1996 Image 1998-1999 Image spanning an eruption in 2007 covering 1995 eruption covering 1998 eruption

7/27 – 10/27, 2007

10 km

Cleveland: Shishaldin: The most active volcano 3rd most active volcano in Aleutians since 1990s. in Aleutians. Moran et al., 2006 20110807 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20110818 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20110829 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20110909 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20110920 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20111001 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20111012 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20111023 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20111103 N Episode Eruption An Cleveland:

Dome growth

Lu and Dzurisin, 2014 ~100 m

20120108 N Episode Eruption An Cleveland: Explosion! Ash Lu and Dzurisin, 2014

~100 m

20120119 N Episode Eruption An Cleveland: Explosion! Ash Lu and Dzurisin, 2014

~100 m

20120210 N Episode Eruption An Cleveland: New dome! New Lu and Dzurisin, 2014

~100 m

Cleveland – a “open-vent” system Episodic Intrusion - an intrinsic feature of Aleutian volcanism  At several Aleutian volcanoes, surface inflation occurs more or less continuously (albeit at time-varying rates) for periods of a few years or longer.  Continuous process of magma formation, ascent, storage in the crust, and eruption. Quasi-Continuous Deformation at Okmok Volcano 1992-1993 1993-1995 1995-1996 1996-1997 1997-1998

1997 eruption

Minor inflation Subsidence 0 28.3 cm 1998-1999 1999-2000 2000-2001 2001-2002 2002-2003

2003-2004 2004-2005 2005-2006 2006-2007 2007-2008

Subsidence Minor inflation No deformation

10 km 0 2.83 cm Episodic Intrusion - an intrinsic feature of Aleutian volcanism  At several Aleutian volcanoes, surface inflation occurs more or less continuously (albeit at time-varying rates) for periods of a few years or longer.  Continuous process of magma formation, ascent, storage in the crust, and eruption.  A larger percentage of Aleutian volcanoes inflate only episodically.  Inflation associated with magma intrusion often is accompanied by seismic swarm.  Intrusion process in other cases can be aseismic. Episodic Intrusions Everywhere Along the Aleutians

6.6 Tanaga: 6.10 Atka Volcanic Center: 6.28 Kupreanof: 6.37 Spurr, Hayes: Atka Volcanic Center

6.20 Makushin:

6.36 Iliamna, Redoubt: 6.37 Strandline Lake: 6.32 Peulik: 6.21 Akutan: Episodic Intrusion - an intrinsic feature of Aleutian volcanism  At several Aleutian volcanoes, surface inflation occurs more or less continuously (albeit at time-varying rates) for periods of a few years or longer.  Continuous process of magma formation, ascent, storage in the crust, and eruption.  A larger percentage of Aleutian volcanoes inflate only episodically.  Inflation associated with magma intrusion often is accompanied by seismic swarm.  Intrusion process in other cases can be aseismic.  Factors that promote the progression of magmatic intrusions into eruptions include  high gas content  rapid gas exsolution  a favorable stress environment (Moran and others, 2011).  Factors that can impede such progress include  magma overpressure below some critical threshold (Pinel and Jaupart, 2004)  high or increasing magma viscosity  slow magma ascent  non-favorable stress environment  buffering effect of geothermal systems (Tait and others, 1989).  Some inflation episodes of Aleutian volcanoes did not happen overnight. Instead, they took weeks to several months.  Often surface inflation episodes end before the associated earthquake swarms end; a behavior that seems consistent with a stalled intrusion continuing to cause seismicity while strain is accommodated in the host rock.  The relatively slow pace of some intrusions, both in the Aleutians and elsewhere, might be a primary control on why they do not culminate in eruptions. A Deep Deformation Source Near a Volcano is not Synonymous With Magma, BUT …

 Most cases of broad surface uplift are attributed to magma intrusion  Most of the model sources are located at or below 5 km BSL, deeper than hydrothermal fluids are thought to exist in active volcanic environments (Fournier, 2007).

 Numerical and conceptual models are simplistic and non-unique. Magmatic systems are inherently complicated, involving physical and chemical interactions among tectonic strain, magma (itself a complex three-phase mixture of melt, crystals, and gas), groundwater, and heterogeneous host rock

 Surface uplift can be caused by pressurization of a magma reservoir without additional input of magma.  Demanding for simultaneous geodetic and precise gravity measurements.

 Nonetheless, the frequent occurrence of precursory uplift at volcanoes that eventually erupt and then subside in a similar pattern is strong circumstantial evidence for the existence of magma reservoirs that are supplied and replenished by intrusions from below, and which occasionally feed intrusions toward the surface. Caldera Systems Are Especially Dynamic  Calderas in Aleutian:  Young calderas in Aleutian: 10  Uplift and subsidence: 4  Persistent subsidence: 6

 Floors of calderas underlain by Emmons Lake Aniakchak partly molten magma bodies, 5 mm/year subsidence 1.5 cm/year subsidence persist for hundreds of thousands (source depth: 3-5 km) of years, tend to move up or down (source depth: ~7 km) with regularity.

 Surface deformation is the norm rather than an exception.

Fisher 1-2 cm/year subsidence (source depth: 3-5 km) Surface Subsidence of Various Kinds is a Common Process at Aleutian Volcanoes • Recent lava flows or pyroclastic flows  Pattern of subsidence mimics the flow distribution  The greatest amount of subsidence occurs where the flow is the thickest • Hydrothermal-system depressurization as a result of cooling and fluid loss  Subsidence fields do not correlate with the distributions of young flows  Modeling suggests source depths in the range 0–4 km BSL • Cooling and fluid loss from crustal magma reservoirs  Subsidence sourced at greater depth than the other two types (~5–12 km BSL)  Source locations for uplift and subsidence are essentially the same  Some of the uplift episodes have culminated in eruptions

Observed Modeled SubsidenceResidual to due Observed deformation Inflation due to source at 5 km geothermal resources

= OkmokVolcano Recheshnoi Volcano 2 km InSAR Source Depth, Geochemistry, Seismicity

BD Seismicity Seismicity (km) Depth

BD – Becharof discontinuity

Buurman et al., 2013 Volcanoes from west to eat Lu and Dzurisin, 2014 Nye, 2008 Tectonic and Structural Influences • Structural influences on magma production rate, composition, and storage  Lack of deep seismicity beneath the eastern part of the arc are due to a diminished flux of magma through the crust relative to the more active central & western parts.  Lesser magma flux results in longer magma residence times in the crust, more fractionation and crustal assimilation, formation of more evolved magmas, and fewer eruptions

• Along-arc changes in stress regime  The horizontal compressional stress is  oblique to the trend of arc over the eastern part of the arc  perpendicular to the trend over the western part of the arc  Magma reservoirs tend to be deeper where regional horizontal compressional stress is greatest

• Differences between oceanic and continental parts of the arc  Magma rising beneath the arc would become neutrally buoyant and pond deeper in continental lithosphere than in denser oceanic lithosphere over the western Aleutian arc

• Along-arc variations in convergence rate, convergence angle, and downdip velocity  No correspondence with source depth Volcano Counts

Aleutian N. C. S. W. Andean Andean Andean Sunda

# of Holocene volcanoes 97 35 69 63 84

# of historically active 52 15 17 27 76 volcanoes # of deformed volcanoes 31 2 4 7 7

# of magmatic deformation 24 1 3 5 6

# of surficial deformation 7 1 1 2 1 Lu, Z. and D. Dzurisin, 2014, “InSAR Imaging of Aleutian Volcanoes: Monitoring a Volcanic Arc from Space”, Springer Praxis Books, Geophysical Sciences, ISBN 978-3-642-00347-9, 390 pp. Thank you!!!

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