Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)

Rooyakkers, Shane M.; Stix, John; Berlo, Kim; Barker, Simon J.

doi:10.1130/b35450.1

Cited by 13 publications

(7 citation statements)

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“…1). Past eruptive activity indicates that Krafla is basalt-dominated (Saemundsson, 1991;Mortensen et al, 2015;Kennedy et al, 2018, and references therein); however, partial melting of basaltic crust has generated rhyolite magma, and a mixed rhyolitebasalt eruption is thought to have been responsible for most of the caldera's subsidence (Marsh et al, 1991;Jónasson, 1994;Rooyakkers et al, 2020). Two other eruptive phases have created rhyolitic domes and ridges both within the caldera and at its margins (Jónasson, 1994;Tuffen and Castro, 2009).…”

Section: Introduction Contextmentioning

confidence: 99%

Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling

et al. 2021

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The unexpected intersection of rhyolitic magma and retrieval of quenched glass particles at the Iceland Deep Drilling Project-1 geothermal well in 2009 at Krafla, Iceland, provide unprecedented opportunities to characterize the genesis, storage, and behavior of subsurface silicic magma. In this study, we analyzed the complete time series of glass particles retrieved after magma was intersected, in terms of distribution, chemistry, and vesicle textures. Detailed analysis of the particles revealed them to represent bimodal rhyolitic magma compositions and textures. Early-retrieved clear vesicular glass has higher SiO2, crystal, and vesicle contents than later-retrieved dense brown glass. The vesicle size and distribution of the brown glass also reveal several vesicle populations. The glass particles vary in δD from −120‰ to −80‰ and have dissolved water contents spanning 1.3−2 wt%, although the majority of glass particles exhibit a narrower range. Vesicular textures indicate that volatile overpressure release predominantly occurred prior to late-stage magma ascent, and we infer that vesiculation occurred in response to drilling-induced decompression. The textures and chemistry of the rhyolitic glasses are consistent with variable partial melting of host felsite. The drilling recovery sequence indicates that the clear magma (lower degree partial melt) overlays the brown magma (higher degree partial melt). The isotopes and water species support high temperature hydration of these partial melts by a mixed meteoric and magmatic composition fluid. The textural evidence for partial melting and lack of crystallization imply that magma production is ongoing, and the growing magma body thus has a high potential for geothermal energy extraction. In summary, transfer of heat and fluids into felsite triggered variable degrees of felsite partial melting and produced a hydrated rhyolite magma with chemical and textural heterogeneities that were then enhanced by drilling perturbations. Such partial melting could occur extensively in the crust above magma chambers, where complex intrusive systems can form and supply the heat and fluids required to re-melt the host rock. Our findings emphasize the need for higher resolution geophysical monitoring of restless calderas both for hazard assessment and geothermal prospecting. We also provide insight into how shallow silicic magma reacts to drilling, which could be key to future exploration of the use of magma bodies in geothermal energy.

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Section: Introduction Contextmentioning

confidence: 99%

Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling

et al. 2021

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“…Some of the largest known ashflow deposits of felsic composition on Earth include the Campanian ignimbrite (∼500 km 3 bulk volume, Fisher et al., 1993), Bishop tuff (∼600 km 3 bulk volume, Hildreth & Mahood, 1986), Fish Canyon tuff (∼500 km 3 bulk volume, Lipman et al., 1973), Peach spring tuff (>1,300 km 3 DRE (dense rock equivalent, Ferguson et al., 2013), Taupo ignimbrites (∼500 km 3 bulk volume, Wilson, 1985), and Rattlesnake tuff (∼280 km 3 DRE, Streck & Grunder, 1995). The modeled deposit volumes greatly exceed the volumes of less common terrestrial mafic ignimbrites, such as Halarauður ignimbrite (∼20 km 3 bulk volume, Rooyakkers et al., 2020), the Okmok PDC deposits (∼29 km DRE, Burgisser, 2005), and Villa Senni ignimbrite (∼30 km 3 DRE, Watkins et al., 2002).…”

Section: Discussionmentioning

confidence: 88%

“…However, the possibility of multiple episodes of explosive activity within the same volcanic zone on Venus is not very clear. Many ignimbrite deposits on Earth are known to have formed from multiple fissures or vents associated with a caldera, in the case of both felsic (Hildreth & Mahood, 1986; Holohan et al., 2008; Jessop et al., 2016; Self et al., 1986; Wilson, 2008) and intermediate to basaltic eruptions (Allen, 2004; Burgisser, 2005; Giordano et al., 2006; Robin et al., 1994; Rooyakkers et al., 2020). In many of these terrestrial examples, PDCs are typically fed from elongated ring‐fracture vents along the caldera boundary.…”

Section: Modeling Dense Pyroclastic Flowsmentioning

confidence: 99%

Modeling the Dynamics of Dense Pyroclastic Flows on Venus: Insights Into Pyroclastic Eruptions

2021

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On Venus, relatively young deposits near volcanic and coronal summits with unique radar characteristics have been proposed to be emplaced by pyroclastic density currents (PDCs). The proposed units are laterally extensive, long‐runout deposits showing moderate to high radar backscatter and circular polarization ratio in 12.6 cm wavelength synthetic aperture radar data. Previous studies have hypothesized that a recent resumption of volcanic activity in the form of PDC‐forming eruptions could have emplaced these deposits. We model the dynamics of dense PDCs using a 2D, depth‐averaged framework focusing on regions where stereo‐derived topography coverage is available; this includes the flanks of Irnini Mons, Anala Mons, Didilia Corona, and Pavlova Corona. Two different mechanisms of initiation which includes impulsive collapse of an eruption column and sustained pyroclastic fountaining are considered. The results emphasize the importance of pyroclastic flow fluidization via high pore pressure in emplacing long‐runout deposits along gently sloping (<2°) volcanic flanks. We also show that collapse of columns >1.2–1.4 km tall as well as pyroclastic fountains lasting >400 s with fountain heights of 50 m are capable of generating pyroclastic flows that could emplace some of the smaller deposits studied. For the large deposits at Irnini Mons, more energetic flows resulting from taller column heights would be necessary; the dynamics of such flows under Venus's conditions are not well understood. Distinguishing between the two initiation styles, that is, column collapse and sustained fountaining is not feasible with currently available datasets and would require higher resolution imagery and topography data.

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“…The Krafla volcanic system consists of a central volcano with a 10 × 8 km caldera of about 110 ka age, partly buried by later lavas (Saemundsson, 1991;Rooyakkers et al, 2020). The caldera is transected by fissure swarms that extend about 45 km to the south and 60 km to the north of the volcano, subparallel to the plate boundary.…”

Section: Kraflamentioning

confidence: 99%

Seismicity of the Northern Volcanic Zone of Iceland

Einarsson

Brandsdóttír

2021

Front. Earth Sci.

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A half century of monitoring of the Northern Volcanic Zone of Iceland, a branch of the North America—Eurasia plate boundary, shows that the seismicity is very unevenly distributed, both in time and space. The four central volcanoes at the boundary, Þeistareykir, Krafla, Fremrinámar, and Askja, show persistent but very low-level seismicity, spatially coinciding with their high-temperature geothermal systems. On their rift structures, on the other hand, seismicity is almost absent, except during rifting episodes. Krafla went through a rifting episode in 1975–1984 with inflation, interrupted by 20 diking events with extensive rifting, eruptive activity, and intense seismicity along an 80 km long section of the rift. During inflation periods, the seismicity was contained within the caldera of the volcano, reflecting the inflation level of the magma chamber. Diking events were marked by seismicity propagating away from the volcano into the fissure swarms to the south or north of the volcano, accompanied by rapid deflation of the caldera magma chamber. These events lasted from 1 day to 3 months, and the dike length varied between 1 and 60 km. The area around the Askja volcano is the only section of the Northern Volcanic Zone that shows persistent moderate seismicity. The largest events are located between fissure swarms of adjacent volcanic systems. Detailed relative locations of hypocenters reveal a system of vertical strike-slip faults, forming a conjugate system consistent with minimum principal stress in the direction of spreading across the plate boundary. A diking event into the lower crust was identified in the adjacent fissure swarm at Upptyppingar in 2007–2008. Four nests of anomalously deep earthquakes (10–34 km) have been identified in the Askja region, apparently associated with the movements of magma well below the brittle-ductile transition. Several processes have been pointed out as possible causes of earthquakes in the deformation zone around the plate boundary. These include inflation and deflation of central volcanoes, intrusion of propagating dikes, both laterally and vertically, strike-slip faulting on conjugate fault systems between overlapping fissure swarms, migration of magma in the lower, ductile crust, and geothermal heat mining.

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Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)

Cited by 13 publications

References 91 publications

Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling

Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling

Modeling the Dynamics of Dense Pyroclastic Flows on Venus: Insights Into Pyroclastic Eruptions

Seismicity of the Northern Volcanic Zone of Iceland

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