Tracy K. P. Gregg

Volcanic eruptions on mid‐ocean ridges: New evidence from the superfast spreading East Pacific Rise, 17°–19°S

uniform sediment cover were recovered from lava that buries older faulted terrain. The boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector, consistent with magmas from two separate reservoirs being erupted in the same event. Chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments. A comparison of our results to global data on submarine mid-ocean ridge eruptions suggests consistent dependencies of erupted volume, activated fissure lengths, and chemical heterogeneity with spreading rate, consistent with expected eruptive characteristics from ridges with contrasting thermal properties and magma reservoir depths. INDEX TERMS: 3035 Marine Geology and Geophysics: Midocean ridge processes; 8414 Volcanology: Eruption mechanisms; 8439 Volcanology: Physics and chemistry of magma bodies; 3655 Mineralogy and Petrology: Major element composition; KEYWORDS: lava flow, chemical heterogeneity, erupted volume, lava morphology, side-scan sonar

Long submarine lava flows: Observations and results from numerical modeling

Long (>100 km) lava flows are relatively common on Mars and Venus and have been identified on the Moon, but they are rarely documented on Earth. However, although ∼75% of the Earths surface is covered by water, only a small percentage of the ocean floor has been investigated at a resolution sufficient to unequivocally identify the boundaries of long submarine lava flows. Even so, basaltic lava flows as long as 110 km have been identified on the deep (>1500 m) seafloor near Hawaii and the East Pacific Rise. Ambient conditions on the deep ocean floor may favor the development of long lava flows for the following reasons. First, high pressures (>15 MPa) keep volatiles dissolved in basaltic lavas, preventing viscosity increases associated with exsolution and vesiculation. Second, seawater rapidly quenches the surface of submarine basalt flows so that an insulating glass layer, 1–5 cm thick, encases submarine flows within seconds after their emplacement. This glass rind effectively insulates the molten flow interior from additional heat loss, making submarine basalt flows behave as well-insulated, subaerial tube-fed flows. Thus, for identical basalt flows emplaced on the deep seafloor and subaerially, a submarine flow could advance farther before stopping. Results of numerical modeling indicate that thin (≤1 m) submarine basalt flows behave similarly to identical subaerial flows, but thicker submarine flows may advance significantly farther than their subaerial counterparts.

Formation of Venusian canali - Considerations of lava types and their thermal behaviors

Because liquid water is unstable at present venusian surface conditions, the discovery of channels (termed “canali”) on Venus thousands of kilometers long was not predicted. Low-viscosity lavas that remain fluid for several thousand kilometers are considered to be the canali-forming agents; possible compositions of venusian canali-forming lavas include komatiite and high-Fe-Ti “lunar”-type basalts. Results of analytical and numerical models of these lavas reveal that total cooling is more efficient on Venus than on Earth, suggesting that venusian lavas rapidly form insulating crusts, and, thus, that the canali lavas were essentially “tube-fed.” The models also reveal that thermal erosion should be less efficient on Venus than on Earth, suggesting that venusian channels are either the product of mechanical (rather than thermal) erosion or constructional processes.

Channeled flow: Analytic solutions, laboratory experiments, and applications to lava flows

Although channeled lava flows are common in basaltic volcanism, relationships between channel morphology, eruption and emplacement parameters, and lava properties are not well understood. Several models have commonly been used to constrain these relations, but they have not been well tested on natural or simulated lava flows over a wide range of parameter space. Here, we test the accuracy and assumptions of a moderately simple analytic rectangular channel solution by comparing the behavior of well-controlled laboratory polyethylene glycol (PEG) channeled flows to the analytic solution for isothermal, steady Newtonian flow in a rectangular channel with constant dimensions. This analytic solution agrees well with laboratory measurements. Volumetric effusion rates (Q; m3 s−1) calculated from the analytical model using measured PEG flows as input yield ratios of Qcalculated/Qpumped of ∼0.2 to 3.6, and flow rates calculated from a best fit surface velocity profile to measured velocities give more accurate ratios of ∼0.8 to 1.2. We find a very weak dependence of solution accuracy on slope, attributable to flow front effects within the laboratory flows. We subsequently apply the solution to several subaerial and submarine terrestrial flows as well as extraterrestrial channeled flows over a wide range of flow parameters. Viscosity ranges and flow rates obtained using measured channel dimensions and assumed lava properties are plausible. Interestingly, the resulting extraterrestrial estimates of viscosities and flow rates tend to fall closer to known terrestrial measurements and estimates of channel flow than to previous planetary estimates. We therefore suggest that the analytic Newtonian rectangular channel flow model is a more appropriate physical model for many channeled terrestrial and planetary flows than the Newtonian infinite sheet flow and approximation to Bingham channel flow widely used previously.

Volcanic investigations of the Puna Ridge, Hawai′i: relations of lava flow morphologies and underlying slopes

Abstract Previous investigators have demonstrated that submarine lava flow morphologies are the result of a complex interplay between lava rheology, effusion rate, and underlying slope. Here, we specifically investigate the relation between underlying slope and submarine lava flow morphology along three study sites of the Puna Ridge, Kilauea Volcano, Hawai′i. Using Electronic Still Camera (ESC) images and detailed bathymetry collected by ARGO-II, we can compare the lava morphology and the associated underlying slope. Our results indicate that rubble is most common on the steepest slopes (≥25°) and that pillowed and lobate flows dominate on slopes ≤20°. Sheet flows were only seen on relatively shallow slopes (≤15°). These observations disagree with the results obtained from previous laboratory analog experiments, suggesting that the laboratory results are directly applicable for lavas emplaced on relatively low (

Using submarine lava pillars to record mid-ocean ridge eruption dynamics

Abstract Submarine lava pillars are hollow, glass-lined, basaltic cylinders that occur at the axis of the mid-ocean ridge, and within the summit calderas of some seamounts. Typically, pillars are ∼1–20 m tall and 0.25–2.0 m in diameter, with subhorizontal to horizontal glassy selvages on their exterior walls. Lava pillars form gradually during a single eruption, and are composed of lava emplaced at the eruption onset as well as the last lava remaining after the lava pond has drained. On the deep sea floor, the surface of a basaltic lava flow quenches to glass within 1 s, thereby preserving information about eruption dynamics, as well as chemical and physical properties of lava within a single eruption. Investigation of different lava pillars collected from a single eruption allows us to distinguish surficial lava-pond or lava-lake geochemical processes from those operating in the magma chamber. Morphologic, major-element, petrographic and helium analyses were performed on portions of three lava pillars formed during the April 1991 eruption near 9°50′N at the axis of the East Pacific Rise. Modeling results indicate that the collected portions of pillars formed in ∼2–5 h, suggesting a total eruption duration of ∼8–20 h. These values are consistent with observed homogeneity in the glass helium concentrations and helium diffusion rates. Major-element compositions of most pillar glasses are homogeneous and identical to the 1991 flow, but slight chemical variations measured in the outermost portions of some pillars may reflect post-eruptive processes rather than those occurring in subaxial magma bodies. Because lava pillars are common at mid-ocean ridges (MORs), the concepts and techniques we present here may have important application to the study of MOR eruptions, thereby providing a basis for quantitative comparisons of volcanic eruptions in geographically and tectonically diverse settings. More research is needed to thoroughly test the hypotheses presented here.

Modeling volcanic processes : the physics and mathematics of volcanism

List of contributors 1. Introduction Sarah Fagents, Tracy Gregg and Rosaly Lopes 2. Magma chamber dynamics and thermodynamics Josef Dufek, Chris Huber and Leif Karlstrom 3. The dynamics of dike propagation Steve Tait and Benoit Taisne 4. Dynamics of magma ascent in the volcanic conduit Helge Gonnermann and Michael Manga 5. Lava flows Andrew Harris 6. Unsteady explosive activity: Strombolian eruptions Mike James, Steve Lane and Bruce Houghton 7. Unsteady explosive activity: Vulcanian eruptions Amanda Clarke 8. Sustained explosive activity: volcanic eruption columns and Hawaiian fountains Andrew Woods 9. Modeling tephra sedimentation from volcanic plumes Costanza Bonadonna and Antonio Costa 10. Pyroclastic density currents Olivier Roche, Jeremy Phillips and Karim Kelfoun 11. Magma-water interactions Ken Wohletz, Bernd Zimanowski and Ralf Buttner 12. Deep sea eruptions Tracy Gregg 13. Magma-ice interactions Lionel Wilson, John Smellie and James Head 14. Modeling lahar behavior and hazards Vernon Manville, Jon Major and Sarah Fagents 15. Introduction to quantitative volcano seismology: fluid-driven sources Bernard Chouet 16. Volcano acoustics Milton Garces, David Fee and Robin Matoza 17. Planetary volcanism Rosaly Lopes, Sarah Fagents, Karl Mitchell and Tracy Gregg Index.

Environmental Effects on Volcanic Eruptions

1. Pyroclastic flows are mixtures of hot gas, ash and other volcanic rocks travelling very quickly down the slopes of volcanoes. Pyroclastic flows are so hot and choking that if one is caught in one the person will certainly be killed. Because these flows are very fast they cannot be out-runned. If a volcano that is known for producing pyroclastic flows is looking like it may erupt soon, the best thing is to evacuate all the people living near the volcano.

A comparison between subaerial and submarine eruptions at Kilauea Volcano, Hawaii: implications for the thermal viability of lateral feeder dikes

Eruption styles on the subaerial East Rift Zone (ERZ) of Kilauea volcano are reviewed and a classification scheme for the different types of eruption is proposed. The various eruption types are produced by differing thermal and driving pressure behaviour in the feeder dikes. Existing evidence is reviewed and new evidence presented of the types and volumes of eruptions on the Puna Ridge, which is the submarine extension of the ERZ. Eruptions on the Puna Ridge fall into the same five classes as, and are of comparable volume to, those on the subaerial ERZ. Evidence is presented which suggests that feeder dikes for Puna Ridge eruptions are more thermally viable than those feeding subaerial eruptions, and this difference causes long-lived, large-volume eruptions to be more common on the Puna Ridge than on the subaerial ERZ. This systematic variation in thermal viability may be due to increased dike width for Puna Ridge dikes or increased pressure gradients driving magma flow. Lateral dike emplacement is common to many basaltic systems including on other Hawaiian volcanoes, in Iceland and at mid-ocean ridges. The systematic trend inferred for the ERZ of Kilauea implies that in the other systems large-volume eruptions may also be more common at great distances than they are close to the magma centre.

Volcanism on Earth’s Seafloor and Venus

The surface of Venus, obscured by dense cloud cover, is similar in many ways to the seafloor that lies hidden beneath the deep waters of Earth’s oceans. Although both are difficult to observe, decades of research indicate that each surface is dominated primarily by basaltic volcanism. This is not surprising as Earth and Venus are similar in size, bulk density, and position in the solar system, and the probability of similar elemental abundances and internal heat sources implies corresponding similarity between their interior melting, magma production, and surface volcanism. Even though Earth’s seafloor and Venus are dissimilar in many ways, both environments are characterized by significantly elevated pressure at the surface resulting, respectively, from the burden imposed by the overlying ocean water and the weight of the dense atmosphere. This provides volcanologists with an excellent opportunity to examine how elevated surface pressure affects the development and behavior of volcanic systems.