Glacial long period seismic events at Katla volcano, Iceland

Jónsdóttir, Kristín; Roberts, Roland; Pohjola, Veijo; Lund, Björn; Shomali, Zaher Hossein; Tryggvason, Ari; Böðvarsson, Reynir

doi:10.1029/2009gl038234

Cited by 24 publications

(51 citation statements)

References 27 publications

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“…Falling ice, like calving and serac collapses, also can generate low‐frequency earthquakes [ Qamar , ; O ’ Neel et al , ; Roux et al , ; Tsai et al , ; Thelen et al , ], and this source can repeat if ice falls in the same location over and over again [e.g., Jonsdottir et al , ], but it is highly unlikely that this is the source of the events in this study because ice is unlikely to fall exactly the same way thousands of times and at very regular intervals.…”

Section: Discussionmentioning

confidence: 99%

Swarms of repeating stick-slip icequakes triggered by snow loading at Mount Rainier volcano

Allstadt

Malone

2014

J. Geophys. Res. Earth Surf.

114

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We have detected over 150,000 small (M < 1) low-frequency (~1-5 Hz) repeating earthquakes over the past decade at Mount Rainier volcano, most of which were previously undetected. They are located high (>3000 m) on the glacier-covered edifice and occur primarily in weeklong to monthlong swarms composed of simultaneous distinct families of events. Each family contains up to thousands of earthquakes repeating at regular intervals as often as every few minutes. Mixed polarity first motions, a linear relationship between recurrence interval and event size, and strong correlation between swarm activity and snowfall suggest the source is stick-slip basal sliding of glaciers. The sudden added weight of snow during winter storms triggers a temporary change from smooth aseismic sliding to seismic stick-slip sliding in locations where basal conditions are favorable to frictional instability. Coda wave interferometry shows that source locations migrate over time at glacial speeds, starting out fast and slowing down over time, indicating a sudden increase in sliding velocity triggers the transition to stick-slip sliding. We propose a hypothesis that this increase is caused by the redistribution of basal fluids rather than direct loading because of a 1-2 day lag between snow loading and earthquake activity. This behavior is specific to winter months because it requires the inefficient drainage of a distributed subglacial drainage system. Identification of the source of these frequent signals offers a view of basal glacier processes, discriminates against alarming volcanic noises, documents short-term effects of weather on the cryosphere, and has implications for repeating earthquakes, in general.

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Section: Discussionmentioning

confidence: 99%

Swarms of repeating stick-slip icequakes triggered by snow loading at Mount Rainier volcano

Allstadt

Malone

2014

J. Geophys. Res. Earth Surf.

114

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“…Seasonal reconfiguration of meltwater drainage above the Katla geothermal field, may create shifting abundance and pressure of meltwater at the glacier base. This could also drive seasonal patterns of shallow low-frequency seismicity and pressure that encourage seismogenic slip at the ice-bedrock boundary in summer months (Jonsdottir et al, 2007(Jonsdottir et al, , 2009). …”

Section: Hydrological Controls On Subglacial Geothermal Volatile Releasementioning

confidence: 98%

Seasonal release of anoxic geothermal meltwater from the Katla volcanic system at Sólheimajökull, Iceland

et al. 2015

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Understanding patterns of geothermal and volcanic activity at many of Iceland's most active volcanic systems is hampered by thick overlying ice, which prevents direct observation and complicates interpretation of geophysical signals. Katla is a prime example, being a large and restless volcanic system covered by the 740 m thick Mýrdalsjökull ice cap, whose eruptions have triggered some of the most powerful known meltwater floods in historical times. To shed new light on geothermal and subglacial hydrological processes at Katla, we have determined the sulphate isotopic composition of a series of glacial meltwater samples discharged from Sólheimajökull, a valley glacier of Mýrdalsjökull, between 2009 and 2012. Dual isotopic analysis of δ 34 S and δ 18 O in dissolved sulphate allows identification of source mixing processes and chemical evolution during subglacial meltwater transport. Strikingly, meltwater δ 18 OSO 4 signatures indicate redox conditions at the glacier bed, which are inverse to those normally encountered at Arctic and Alpine glaciers. Discharge of reduced, anoxic meltwater in summer, rather than winter, points towards seasonal release of geothermally derived volatile gases. We attribute this to headward expansion of the channelized subglacial drainage system during the summer melt season, accessing key areas of geothermal activity within the Katla caldera. Volatile release may be further enhanced by unloading of overburden pressure due to snowpack melting in the summer season. In winter, restriction of subglacial channels to lower elevations effectively seals geothermal fluids and dissolved gases beneath the ice cap, with only sporadic release permitted by periodic increases in subglacial water pressure. When the subglacial drainage configuration permits access to key geothermal areas, sulphate isotopic signatures thereby form sensitive indicators of geothermal activity occurring deep beneath the Mýrdalsjökull ice cap.

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“…Some enigmatic low‐period glacial events (hereafter “LP”) could be easily confused with volcanic activity [ St. Lawrence and Qamar , ]. This is particularly dangerous because LP seismic events are often interpreted as eruptive precursors; hence, misidentification could lead to false alarms and unnecessary evacuations [ Jónsdóttir et al , ]. Thus, it is of crucial importance to accurately distinguish between these event types, which have very different origins but comparable seismic signatures.…”

Section: Glacier‐covered Volcanoes and Lp Eventsmentioning

confidence: 99%

“…LP earthquakes of glacial origin can be caused by ice falls [i.e., a single force mechanism; Jónsdóttir et al , ], resonant water‐filled ice cavities, or sudden changes in water flow rate [ St. Lawrence and Qamar , ; Métaxian , ].…”

Section: Glacier‐covered Volcanoes and Lp Eventsmentioning

confidence: 99%

Cryoseismology

Podolskiy

Walter

2016

Reviews of Geophysics

217

209

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The last decade witnessed an explosion in yearly number of publications on passive glacier seismology. The seismic signals from a wide range of glacier‐related processes fill a broad band of frequencies (from 10−3 to 102 Hz) and moment magnitudes (from M–3 to M7) providing a fresh and unprecedented view on fundamental processes in the cryosphere. New insights into basal motion, iceberg calving, glacier, iceberg, and sea ice dynamics, and precursory signs of unstable glaciers and ice structural changes are being discovered with seismological techniques. These observations offer an invaluable foundation for understanding ongoing environmental changes and for future monitoring of ice bodies worldwide. In this review we discuss seismic sources in the cryosphere as well as research challenges for the near future. The field of glacier seismology is evolving so rapidly that some parts of this review will likely soon be outdated. Nevertheless, given an overwhelming number of recent publications and rapidly growing seismic data volumes provided by modern seismic installations in polar and mountain regions, this introduction to cryosphere seismicity aims to serve as a timely and comprehensive reference for glaciologists and seismologists.

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Glacial long period seismic events at Katla volcano, Iceland

Cited by 24 publications

References 27 publications

Swarms of repeating stick-slip icequakes triggered by snow loading at Mount Rainier volcano

Swarms of repeating stick-slip icequakes triggered by snow loading at Mount Rainier volcano

Seasonal release of anoxic geothermal meltwater from the Katla volcanic system at Sólheimajökull, Iceland

Cryoseismology

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