R. J. Carey

Pigeonholing pyroclasts: Insights from the 19 March 2008 explosive eruption of Kīlauea volcano

We think, conventionally, of volcanic explosive eruptions as being triggered in one of two ways: by release and expansion of volatiles dissolved in the ejected magma (magmatic explosions) or by transfer of heat from magma into an external source of water (phreatic or phreatomagmatic explosions). We document here an event where neither magma nor an external water source was involved in explosive activity at Kīlauea. Instead, the eruption was powered by the expansion of decoupled magmatic volatiles released from deeper magma, which was not ejected by the eruption, and the trigger was a collapse of near-surface wall rocks that then momentarily blocked that volatile flux. Mapping of the advected fall deposit a day after this eruption has highlighted the difficulty of constraining deposit edges from unobserved or prehistoric eruptions of all magnitudes. Our results suggest that the dispersal area of advected fall deposits could be miscalculated by up to 30% of the total, raising issues for accurate hazard zoning and assessment. Eruptions of this type challenge existing classification schemes for pyroclastic deposits and explosive eruptions and, in the past, have probably been interpreted as phreatic explosions, where the eruptive mechanism has been assumed to involve flashing of groundwater to steam.

On the fate of pumice rafts formed during the 2012 Havre submarine eruption

Pumice rafts are floating mobile accumulations of low-density pumice clasts generated by silicic volcanic eruptions. Pumice in rafts can drift for years, become waterlogged and sink, or become stranded on shorelines. Here we show that the pumice raft formed by the impressive, deep submarine eruption of the Havre caldera volcano (Southwest Pacific) in July 2012 can be mapped by satellite imagery augmented by sailing crew observations. Far from coastal interference, the eruption produced a single >400 km2 raft in 1 day, thus initiating a gigantic, high-precision, natural experiment relevant to both modern and prehistoric oceanic surface dispersal dynamics. Observed raft dispersal can be accurately reproduced by simulating drift and dispersal patterns using currents from an eddy-resolving ocean model hindcast. For future eruptions that produce potentially hazardous pumice rafts, our technique allows real-time forecasts of dispersal routes, in addition to inference of ash/pumice deposit distribution in the deep ocean.

Convection in a volcanic conduit recorded by bubbles

Microtextures of juvenile pyroclasts from Kīlauea’s (Hawai‘i) early A.D. 2008 explosive activity record the velocity and depth of convection within the basaltic magma-filled conduit. We use X-ray microtomography (μXRT) to document the spatial distribution of bubbles. We find small bubbles (radii from 5 μm to 70 μm) in a halo surrounding larger millimeter-size bubbles. This suggests that dissolved water was enriched around the larger bubbles—the opposite of what is expected if bubbles grow as water diffuses into the bubble. Such volatile enrichment implies that the volatiles within the large bubbles were redissolving into the melt as they descended into the conduit by the downward motion of convecting magma within the lava lake. The thickness of the small bubble halo is ∼100–150 μm, consistent with water diffusing into the melt on time scales on the order of 103 s. Eruptions, triggered by rockfall, rapidly exposed this magma to lower pressures, and the haloes of melt with re-dissolved water became sufficiently supersaturated to cause nucleation of the population of smaller bubbles. The required supersaturation pressures are consistent with a depth of a few hundred meters and convection velocities of the order of 0.1 m s−1, similar to the circulation velocity observed on the surface of the Halema‘uma‘u lava lake.

Discovery of the largest historic silicic submarine eruption

It was likely twice the size of the renowned Mount St. Helens eruption of 1980 and perhaps more than 10 times bigger than the more recent 2010 Eyjafjallajokull eruption in Iceland. However, unlike those two events, which dominated world news headlines, in 2012 the daylong submarine silicic eruption at Havre volcano in the Kermadec Arc, New Zealand (Figure 1a; ~800 kilometers north of Auckland, New Zealand), passed without fanfare. In fact, for a while no one even knew it had occurred.

Pyroclastic Fall Deposits

Abstract Pyroclastic fall deposits form during explosive eruptions by the sedimentation of pyroclasts through the atmosphere from an eruption jet and/or plume. They are the simplest of pyroclastic products and yet they offer the clearest unequivocal insights into eruption, transport, and depositional processes. Their value within physical volcanology lies in their simplicity and in the ease with which their properties can be measured on three characteristic length scales, and used to infer eruption parameters. On the longest length scales, the geometry or “footprint” of a fall deposit constrains quantitatively the discharge rates. On outcrop scale, distinctive thinning and fining properties characterize deposits produced by different eruption styles and intensities. On the scale of single pyroclasts, the size distribution of the pyroclasts and their aerodynamic properties strongly influence transport process. Falling pyroclasts are fractionated during their transport through air (and sometimes also through water). Integrating grain size data produces a “whole deposit” grain size distribution that reflects principally the nature and mechanical efficiency of the fragmentation process. Particle morphology is also a strong indication of the fragmentation style and melt rheology.

Contrasting styles of welding observed in the proximal Askja 1875 eruption deposits II: Local welding

Welded fall deposits on the northern caldera rim at Askja volcano are associated with the Plinian phase of the 1875 eruption. Two welding units occur within the proximal Plinian fall centered on stratigraphic sub-units which, where non-welded, are poorly sorted and ash-rich with high abundances of fluidal and needle-like ash particles. Welding has formed due to two discrete processes; a) the sintering of hot ash and lapilli which forms the two distinct units that are laterally continuous on distance scales of tens of meters (termed ‘regional welding’), and b) creation of welding halos enclosing large, dense, discrete, nonto poorly vesicular spatter bombs that are up to 9 m in diameter (termed ‘local welding’). This paper is concerned with the nature of regional welding and the companion paper (this issue) focuses on the phenomenon of local welding. Three case studies documenting the range of welding patterns observed in regional welding are presented here. Vertical and lateral profiles of welding intensity, together with the deposit characteristics reveal that welding could only occur when the accumulation rates were sufficient and that grain size and thickness are second order factors facilitating welding. Rapid and reversible shifts in both thickness and welding grade are observed on a ~10 m scale laterally along the caldera rim suggesting considerable unsteadiness of the transport regime, which promoted localized fluctuations of the accumulation rate. The welded deposits prompt re-examination of both the dynamics of the Plinian phase of the 1875 eruption and the distribution of source vents. The dispersal of the welding units is not compatible with deposition from the full height of the Plinian plume. Similarly to the ultra-proximal deposits of Novarupta or Tarawera, these clasts probably fell from heights of hundreds of meters to b4 km, retaining sufficient heat to weld after deposition. The E–W elongated distribution of the welded units is also not compatible with a single source vent, and favors several vents that were in a fountaining phase, and located adjacent to the northern rim.

'Inheritance': An influence on the particle size of pyroclastic deposits

The size distribution of particles in pyroclastic fall deposits has been interpreted as a strong indication of efficiency of the fragmentation process during the parent explosions. Fall deposits, however, contain two distinct populations of pyroclasts: juvenile, i.e., magmatic clasts fragmented from the magma, and wall-rock particles derived from walls of the vent and volcanic conduit. While sizes and shapes of the former are always sensitive indicators of eruptive processes, properties of the wall-rock population may reflect various external influences. Here we describe how the wall-rock component of a powerful historical eruption largely inherited its size distribution from properties of the host rocks, and how this, in turn, strongly biases the entire deposit grain size distribution of the near-vent deposits. The use of wall-rock particles to infer style of fragmentation and eruption must always be coupled with other independent lines of evidence.

Hawaiian volcanoes : from source to surface

Contributors vii Preface xi About the Companion Website xiii 1. How and Why Hawaiian Volcanism Has Become Pivotal to Our Understanding of Volcanoes from Their Source to the Surface 1 Michael O. Garcia 2. Seismic Constraints on a Double Layered Asymmetric Whole Mantle Plume Beneath Hawai I 19 Cheng Cheng, Richard M. Allen, Rob W. Porritt, and Maxim D. Ballmer 3. Asymmetric Dynamical Behavior of Thermochemical Plumes and Implications for Hawaiian Lava Composition 35 Maxim D. Ballmer, Garrett Ito, and Cheng Cheng 4. Major Element and Isotopic Variations in Mauna Loa Magmas over 600 ka: Implications for Magma Generation and Source Lithology as Mauna Loa Transits the Hawaiian Plume 59 J. Michael Rhodes 5. Lithium Isotopic Signature of Hawaiian Basalts 79 Lauren Harrison, Dominique Weis, Diane Hanano, and Elspeth Barnes 6. Onset of Rejuvenated Stage Volcanism and the Formation of L hu e Basin: Kaua i Events That Occurred 3 4 Million Years Ago 105 David R. Sherrod, Scot K. Izuka, and Brian L. Cousens 7. Evidence for Large Compositional Ranges in Coeval Melts Erupted from K lauea s Summit Reservoir 125 Rosalind T. Helz, David A. Clague, Larry G. Mastin, and Timothy R. Rose 8. Petrologic Testament to Changes in Shallow Magma Storage and Transport During 30+ Years of Recharge and Eruption at K lauea Volcano, Hawai I 147 Carl R. Thornber, Tim R. Orr, Christina Heliker, and Richard P. Hoblitt 9. Shallow Magma Storage at Piton de la Fournaise Volcano After 2007 Summit Caldera Collapse Tracked in Pele s Hairs 189 Andrea Di Muro, Thomas Staudacher, Valerie Ferrazzini, Nicole Metrich, Pascale Besson, Christine Garofalo, and Benoit Villemant 10. Analysis of Seismicity Rate Changes and Tilt During Early Episodic Fountaining Stage of Pu u O o , Hawai i, Eruption: Implications for Magma Storage and Transport 213 Harmony V. Colella and James H. Dieterich 11. Episodic Deflation Inflation Events at Kilauea Volcano and Implications for the Shallow Magma System 229 Kyle R. Anderson, Michael P. Poland, Jessica H. Johnson, and Asta Miklius 12. Crustal Stress and Structure at K lauea Volcano Inferred from Seismic Anisotropy 251 Jessica H. Johnson, Donald A. Swanson, Diana C. Roman, Michael P. Poland, and Weston A. Thelen 13. Delicate Balance of Magmatic Tectonic Interaction at K lauea Volcano, Hawai i, Revealed from Slow Slip Events 269 Emily K. Montgomery Brown, Michael P. Poland, and Asta Miklius 14. From Reservoirs and Conduits to the Surface: Review of Role of Bubbles in Driving Basaltic Eruptions 289 Sylvie Vergniolle and Yves Gaudemer 15. Insights Into Mixing, Fractionation, and Degassing of Primitive Melts at K lauea Volcano, Hawai I 323 Marie Edmonds, Isobel Sides, and John Maclennan 16. Reticulite Producing Fountains From Ring Fractures in K lauea Caldera ca. 1500 CE 351 Michael May, Rebecca J. Carey, Donald A. Swanson, and Bruce F. Houghton 17. Hawaiian Fissure Fountains: Quantifying Vent and Shallow Conduit Geometry, Episode 1 of the 1969 1974 Mauna Ulu Eruption 369 Carolyn Parcheta, Sarah Fagents, Donald A. Swanson, Bruce F. Houghton, and Todd Ericksen 18. K lauea s 5 9 March 2011 Kamoamoa Fissure Eruption and Its Relation to 30+ Years of Activity From Pu u O o 393 Tim R. Orr, Michael P. Poland, Matthew R. Patrick, Weston A. Thelen, A. Jeff Sutton, Tamar Elias, Carl R. Thornber, Carolyn Parcheta, and Kelly M. Wooten 19. Onset of a Basaltic Explosive Eruption From Kilauea s Summit in 2008 421 Rebecca J. Carey, Lauren Swavely, Donald A. Swanson, Bruce F. Houghton, Tim R. Orr, Tamar Elias, and A. Jeff Sutton 20. Primitive Components, Crustal Assimilation, and Magmatic Degassing During the Early 2008 Kilauea Summit Eruptive Activity 439 Michael C. Rowe, Carl R. Thornber, and Tim R. Orr 21. FLOWGO 2012: An Updated Framework for Thermorheological Simulations of Channel Contained Lava 457 Andrew J. L. Harris and Scott K. Rowland 22. Lava Flows in 3D: Using Airborne Lidar and Preeruptive Topography To Evaluate Lava Flow Surface Morphology and Thickness in Hawai I 483 Hannah R. Dietterich, S. Adam Soule, Katharine V. Cashman, and Benjamin H. Mackey 23. Are Piton de la Fournaise (La Reunion) and K lauea (Hawai i) Really Analog Volcanoes ? 507 Aline Peltier, Michael P. Poland, and Thomas Staudacher 24. Points Requiring Elucidation About Hawaiian Volcanism 533 Michael P. Poland Index 563

The largest deep-ocean silicic volcanic eruption of the past century

A submersible study of the products of a large submarine eruption demonstrates the influence of the ocean on eruption dynamics. The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production.

Stronger or longer: Discriminating between Hawaiian and Strombolian eruption styles

The weakest explosive volcanic eruptions globally, Strombolian explosions and Hawaiian fountaining, are also the most common. Yet, despite over a hundred years of observations, no classifications have offered a convincing, quantitative way of demarcating these two styles. New observations show that the two styles are distinct in their eruptive time scale, with the duration of Hawaiian fountaining exceeding Strombolian explosions by ∼300–10,000 s. This reflects the underlying process of whether shallow-exsolved gas remains trapped in the erupting magma or is decoupled from it. We propose here a classification scheme based on the duration of events (brief explosions versus prolonged fountains) with a cutoff at 300 s that separates transient Strombolian explosions from sustained Hawaiian fountains.