Geology topics

Don Swanson

Publications and source records attributed to Don Swanson.

32 records · Page 2Linked to original sources

USGS2014

Constraining explosive volcanism: Subjective choices during estimates of eruption magnitude

When estimating the magnitude of explosive eruptions from their deposits, individuals make three sets of critical choices with respect to input data: the spacing of sampling sites, the selection of contour intervals to constrain the field measurements, and the hand contouring of thickness/isomass data, respectively. Volcanologists make subjective calls, as there are no accepted published protocols and few accounts of how these choices will impact estimates of eruption magnitude. Here, for the first time, we took a set of unpublished thickness measurements from the 1959 Kīlauea Iki pyroclastic fall deposit and asked 101 volcanologists worldwide to hand contour the data. First, there were surprisingly consistent volume estimates across maps with three different sampling densities. Second, the variability in volume calculations imparted by individuals’ choices of contours is also surprisingly low and lies between s  = 5 and 8 %. Third, volume estimation is insensitive to the extent to which different individuals “smooth” the raw data in constructing contour lines. Finally, large uncertainty is associated with the construction of the thinnest isopachs, which is likely to underestimate the actual trend of deposit thinning. The net result is that researchers can have considerable confidence in using volume or dispersal data from multiple authors and different deposits for comparative studies. These insights should help volcanologists around the world to optimize design and execution of field-based studies to characterize accurately the volume of pyroclastic deposits.

Bulletin of Volcanology↗

USGS2014

Magma mixing and high fountaining during the 1959 Kīlauea Iki eruption, Hawai‘i

The 1959 Kīlauea Iki eruption provides a unique opportunity to investigate the process of shallow magma mixing, its impact on the magmatic volatile budget and its role in triggering and driving episodes of Hawaiian fountaining. Melt inclusions hosted by olivine record a continuous decrease in H 2 O concentration through the 17 episodes of the eruption, while CO 2 concentrations correlate with the degree of post-entrapment crystallization of olivine on the inclusion walls. Geochemical data, when combined with the magma budget and with contemporaneous eruption observations, show complex mixing between episodes involving hot, geochemically heterogeneous melts from depth, likely carrying exsolved vapor, and melts which had erupted at the surface, degassed and drained-back into the vent. The drained-back melts acted as a coolant, inducing rapid cooling of the more primitive melts and their olivines at shallow depths and inducing crystallization and vesiculation and triggering renewed fountaining. A consequence of the mixing is that the melts became vapor-undersaturated, so equilibration pressures cannot be inferred from them using saturation models. After the melt inclusions were trapped, continued growth of vapor bubbles, caused by enhanced post-entrapment crystallization, sequestered a large fraction of CO 2 from the melt within the inclusions. This study, while cautioning against accepting melt inclusion CO 2 concentrations “as measured” in mixed magmas, also illustrates that careful analysis and interpretation of post-entrapment modifications can turn this apparent challenge into a way to yield novel useful insights into the geochemical controls on eruption intensity.

Earth and Planetary Science Letters↗

USGS2014

Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i

The subaerial eruptive activity at Kīlauea Volcano (Hawai‘i) for the past 2500 yr can be divided into 3 dominantly effusive and 2 dominantly explosive periods, each lasting several centuries. The prevailing style of eruption for 60% of this time was explosive, manifested by repeated phreatic and phreatomagmatic activity in a deep summit caldera. During dominantly explosive periods, the magma supply rate to the shallow storage volume beneath the summit dropped to only a few percent of that during mainly effusive periods. The frequency and duration of explosive activity are contrary to the popular impression that Kīlauea is almost unceasingly effusive. Explosive activity apparently correlates with the presence of a caldera intersecting the water table. The decrease in magma supply rate may result in caldera collapse, because erupted or intruded magma is not replaced. Glasses with unusually high MgO, TiO 2 , and K 2 O compositions occur only in explosive tephra (and one related lava flow) and are consistent with disruption of the shallow reservoir complex during caldera formation. Kīlauea is a complex, modulated system in which melting rate, supply rate, conduit stability (in both mantle and crust), reservoir geometry, water table, and many other factors interact with one another. The hazards associated with explosive activity at Kīlauea’s summit would have major impact on local society if a future dominantly explosive period were to last several centuries. The association of lowered magma supply, caldera formation, and explosive activity might characterize other basaltic volcanoes, but has not been recognized.

Hawai'i↗

USGS2013

Pushing the Volcanic Explosivity Index to its limit and beyond: Constraints from exceptionally weak explosive eruptions at Kīlauea in 2008

Estimating the mass, volume, and dispersal of the deposits of very small and/or extremely weak explosive eruptions is difficult, unless they can be sampled on eruption. During explosive eruptions of Halema‘uma‘u Crater (Kīlauea, Hawaii) in 2008, we constrained for the first time deposits of bulk volumes as small as 9–300 m 3 (1 × 10 4 to 8 × 10 5 kg) and can demonstrate that they show simple exponential thinning with distance from the vent. There is no simple fit for such products within classifications such as the Volcanic Explosivity Index (VEI). The VEI is being increasingly used as the measure of magnitude of explosive eruptions, and as an input for both hazard modeling and forecasting of atmospheric dispersal of tephra. The 2008 deposits demonstrate a problem for the use of the VEI, as originally defined, which classifies small, yet ballistic-producing, explosive eruptions at Kīlauea and other basaltic volcanoes as nonexplosive. We suggest a simple change to extend the scale in a fashion inclusive of such very small deposits, and to make the VEI more consistent with other magnitude scales such as the Richter scale for earthquakes. Eruptions of this magnitude constitute a significant risk at Kīlauea and elsewhere because of their high frequency and the growing number of “volcano tourists” visiting basaltic volcanoes.

Hawaii↗

USGS2011

Small explosion from new vent at Kilauea’s summit

At 0258 Hawaii‐Aleutian Standard Time (HST) on 19 March 2008, a small explosion scattered altered and fresh lithic debris across a 40‐hectare area at the summit of Kilauea volcano. This explosion, the first recorded there since 1924, issued from a vent about 35 meters wide along the east wall of Halema'uma'u Crater. Ballistic fragments—the largest measuring nearly 1 meter across—were propelled upward more than 70 meters onto the Halema'uma'u crater rim. Coarse ash and centimeter‐size lithic debris covered part of Crater Rim Drive, and fine ash was deposited farther than 30 kilometers to the southwest.

Hawaii↗

USGS2011

Buckets of ash track tephra flux from Halema'uma'u Crater, Hawai'i

The 2008–2009 eruption at Kīlauea Volcano's summit made news because of its eight small discrete explosive eruptions and noxious volcanic smog (vog) created from outgassing sulfur dioxide. Less appreciated is the ongoing, weak, but continuous output of tephra, primarily ash, from the new open vent in Halema'uma'u Crater. This tephra holds clues to processes causing the eruption and forming the new crater-in-a-crater, and its flux is important to hazard evaluations. The setting of the vent–easily accessible from the Hawaiian Volcano Observatory (HVO)—is unusually favorable for neardaily tracking of tephra mass flux during this small prolonged basaltic eruption. Recognizing this, scientists from HVO are collecting ash and documenting how ejection masses, components, and chemical compositions vary through time.

Hawai'i↗

USGS2011

Shallow degassing events as a trigger for very-long-period seismicity at Kilauea Volcano, Hawaii

The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately 1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates that the VLP is caused by forces—sourced at or very near the lava free surface due to degassing—transmitted down the magma column and coupling to the surrounding rock at 1 km depth.

Hawaii↗

USGS2011

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.

Hawaii↗

USGS2010

Eruption dynamics of Hawaiian-style fountains: The case study of episode 1 of the Kilauea Iki 1959 eruption

Hawaiian eruptions are characterized by fountains of gas and ejecta, sustained for hours to days that reach tens to hundreds of meters in height. Quantitative analysis of the pyroclastic products from the 1959 eruption of Kīlauea Iki, Kīlauea volcano, Hawai‘i, provides insights into the processes occurring during typical Hawaiian fountaining activity. This short-lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption, the focus of this paper. Microtextural analysis of Hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit. Vesicle number densities for all clasts are high (10 6 –10 7 cm −3 ). Post-fragmentation expansion of bubbles within the thermally-insulated fountain overprints the pre-fragmentation bubble populations, leading to a reduction in vesicle number density and increase in mean vesicle size. However, early quenched rims of some clasts, with vesicle number densities approaching 10 7 cm −3 , are probably a valid approximation to magma conditions near fragmentation. The extent of clast evolution from low vesicle-to-melt ratio and corresponding high vesicle number density to higher vesicle-to-melt ratio and lower vesicle-number density corresponds to the length of residence time within the fountain.

Hawaii↗

USGS1987

The significance of observations at active volcanoes; A review and annotated bibliography of studies at Kilauea and Mount St. Helens

Study of active volcanoes yields information of much broader significance than to only the discipline of volcanology. Some applications are 1) interpretation of lava-flow structures, stratigraphic complexities, and petrologic relations in older volcanic units; 2) interpretation of bulk properties of the mantle and constraints on partial melting and deep magma transport; 3) interpretation of geophysical characteristics of potentially active volcanic systems; 4) direct determination of physical properties of molten and solidified basalt, and of intensive variables (e.g., oxygen fugacity and temperature) accompanying cooling and crystallization; 5) quantitative assessment of crystal fractionation and magma mixing, 6) tests of theoretical and experimental geochemical, geophysical, and rheologic models of volcanic behavior; and 7) confirmation in nature of laboratory experiments related to crystallization in igneous systems. The critical factors that make real-time study of volcanic activity valuable are that the location and timing of events are known, and that molten rock and gases are available for direct observation and sampling for subsequent study. Observations made over a period of time make it possible to calculate rates of magma transport, storage, and crystallization, as well as to quantitatively determine elastic and inelastic deformation and the build up and decay of stress within the active volcanic system. Discussion of these topics is keyed to an annotated bibliography from which quantitative information on properties and processes may be obtained. Emphasis is on Hawaii's active basaltic volcanoes for which the most information is available. Additional references are made to research at Mount St. Helens, one of the first real-time studies of an active volcano of dacitic composition.

Hawaii, Washington↗

USGS1986

Regional correlation of Grande Ronde basalt flows, Columbia River basalt group, Washington, Oregon, and Idaho (USA)

The tholeiitic flood basalts of the Columbia River Basalt Group of middle and late Miocene age cover more than 200,000 km 2 in Washington, Oregon, and Idaho. The most voluminous formation of the Group, the Grande Ronde Basalt, erupted for 2 m.y. from north-northwest-trending fissure systems concentrated in southeast Washington and adjacent Oregon and Idaho. Four magnetostratigraphic units (designated R 1 , N 1 , R 2 , and N 2 from oldest to youngest) are recognized on the basis of polarity in the Grande Ronde and provide the broad stratigraphic framework for the formation. In this study, major-element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the Grande Ronde Basalt on a regional scale. Systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings, which are distinguished primarily by small but significant variations in MgO, TiO 2 , and P 2 O 5 content. In addition, four minor chemical types local to the eastern part of the province have been identified. Feeder dikes of each chemical type have also been located. Flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical-stratigraphic subunits. These subunits consist of several flows collectively 30–150 m thick. Subunits of most chemical types are repeated at irregular intervals throughout the formation; no progressive chemical trend occurs within the Grande Ronde. Many of the chemical-stratigraphic subunits extend to the margins of the province, although most are confined to the source region in eastern Washington. Although the total number of subunits is less in the west away from the fissure systems, the total thicknesses of the N 2 and R 2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern Washington. The greatest thicknesses occur in the central part of the province within the Pasco basin. The distribution of basalt relative to the location of vents, as well as the relative east-west thicknesses, suggests that basalt flowed hundreds of kilometres westward during the most voluminous Grande Ronde eruptions, ponding against the irregular margin of the Cascade Range and being diverted through the ancestral Columbia Gorge toward the Washington-Oregon coast. Between these huge sheetflood events, smaller eruptions blanketed areas within the source region, and ongoing regional subsidence created a shallow westward-draining basin in the center of the province.

Idaho, Oregon, Washington↗

USGS1975

Chemical compositions of Kilauea east-rift lava, 1968–1971

The major element chemical compositions of lava from four eruptions on the east rift zone of Kilauea between August 1968 and October 1971 reflect three petrologic processes: Production of chemically distinct batches of magma in the mantle. Separation of olivine, augite, and plagioclase from liquid during flow in the rift-zone conduits. Mixing of different magmas during ascent to the surface. Chemically none of the four Kilauea east-rift eruptions matches the preceding summit eruption in Halemaumau that ended in July 1968. The Mauna Ulu eruption, May 1969 to October 1971 (the last of flie east-rift eruptions), can be divided into five olivine-controlled and chemically distinct variants. Three of these characterize the first seven months of the eruption and are closest in composition to the 1967–8 Halemaumau eruption. Variants 4 and 5 were erupted later and have compositions that are distinctly different from that of the 1967–8 eruption. Major differences are higher Al 2 O 3 (0·15–0·23 per cent), and lower K 2 O (0·07–0·10 per cent) and TiO 2 (0·12–0·23 per cent) in variants 4 and 5 at the same MgO content. Some lavas from eruptions in August and October 1968 and February 1969, have olivine-controlled magma compositions that are identical to mixtures of Mauna Ulu variants 1–3 and the 1967–8 composition. This observation fits an hypothesis advanced earlier by T. L. Wright and R. S. Fiske that magmas in the central magma chamber become mixed with magmas in the rift zone and can be identified as mixing components of rift eruption magmas before they appear as distinctive magmas in summit eruptions. Lavas representing mixing of olivine-controlled magma with differentiated magma were erupted in October 1968, February 1969, and in May and December 1969. The changes in amount of K 2 O and TiO 2 during the latter part of the 1969–71 Mauna Ulu eruption are the reverse of the overall secular change in composition of Kilauea summit lavas from pre-1750 through 1967–8. The K 2 O and TiO 2 contents of the latest overflows during the 1969–71 Mauna Ulu eruption (April 1971) are comparable to that of lava erupted at Kilauea summit prior to 1750. The changing chemistry of Kilauea magma is found to be of use as a ‘tracer’ in the complex Kilauea conduit system. Application of these data to older lava sequences is difficul because of the complexity of the processes controlling lava composition and the absence of detailed information about the time-space chemical variation during individual eruptions.

Hawaii↗

USGS1973

Chemical variation related to the stratigraphy of the Columbia River basalt

Study of major element chemical analyses of Columbia River basalt leads to a grouping of most of the analyses into 11 chemical types which are distinguished with little overlap on a SiO 2 -MgO variation diagram. Other diagnostic variation diagrams are total iron (‘FeO’)-MgO, K 2 O-MgO, and TiO 2 -MgO. A four-unit informal stratigraphy has been adopted in order to define the relations between chemical composition and stratigraphic position. From oldest to youngest, the four stratigraphic units are (1) lower basalt of Bond (1963) and Picture Gorge basalt, (2) lower Yakima basalt, (3) middle Yakima basalt, and (4) upper Yakima basalt. Most of the Picture Gorge and lower basalt flows are relatively rich in MgO (approximately 4.5 to 7.1 percent) and are distinguished by intermediate SiO 2 relative to MgO. Furthermore, the Picture Gorge basalt generally has low K 2 O relative to MgO. The lower Yakima basalt consists almost entirely of flows with relatively low MgO content (approximately 3.0 to 5.5 percent) and with the highest SiO 2 relative to MgO of any flows of the Columbia River basalt. The middle Yakima basalt contains flows of three distinct chemical types, which together cover the same MgO range as the lower Yakima flows but which have considerably lower SiO 2 and higher ‘FeO’ and TiO 2 relative to MgO. Flows in the upper Yakima basalt are of diverse composition; two of the youngest flows are distinguished by having the lowest SiO 2 and highest ‘FeO’, TiO 2 , and P 2 O 5 relative to MgO of any analyzed Columbia River basalt. Flows of one or more chemical types may form the dominant lithology in a stratigraphic unit, but single flows of the same chemical types may occur in any stratigraphic unit. Some lava sampled in the eastern part of the plateau has more TiO 2 than does lava of otherwise similar composition sampled in the western part of the plateau. This is tentatively interpreted as reflecting a heterogeneous composition for the mantle beneath the Columbia Plateau.

Oregon, Washington↗

USGS1973

Flow of lava into the sea, 1969–1971, Kilauea Volcano, Hawaii

Lava from the Mauna Ulu eruption on Kilauea Volcano entered the sea on the south coast of the Island of Hawaii three times from 1969 to 1971. Two of these flows were investigated underwater by divers, one while lava was actively flowing. The June 1969 flow entered the sea as a narrow flow of aa. Below sea level, the flow maintained continuity and flowed at least several hundred meters to a depth beyond 70 m. Several cylindrical flow lobes about 1 m in diameter and about 10 to 15 m long emerged from the side of the aa flow at a depth of about 25m. Underwater investigations, combined with subaerial observations, revealed that the March–May 1971 flow produced a distinct lava delta composed of subaerial pahoehoe lava resting on a submarine sequence of steeply dipping foreset-bedded volcanic sand and rubble that includes conformably dipping cylindrical lava tongues. Most of the pahoehoe streams pouring over the sea cliff are quenched and shattered to glassy sand and rubble that in turn is further fragmented by vigorous wave action and avalanching. In some places, however, larger pahoehoe flows maintain coherence across the cliff and through the surf zone to feed submarine lava tongues. Underwater, these active lava tongues emitted a roaring noise as lava flowed inside their outer black glassy walls. Periodically, cracks exposed the brightly incandescent lava within, and pillow-like buds and toes grew from the top and sides of the lava tongue. Only a small amount of steam was generated underwater. Water temperature close to the active tongues was elevated only 2.5°C.

Hawaii↗