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1.
Mount Erebus, a large intraplate stratovolcano dominating Ross Island, Antarctica, hosts the world's only active phonolite lava lakes. The main manifestation of activity at Erebus volcano in December 2004 was as the presence of two convecting lava lakes within an inner crater. The long-lived Ray Lake, ~ 1400 m2 in area, was the site of up to 10 small Strombolian eruptions per day. A new but short-lived, ~ 1000–1200 m2 lake formed at Werner vent in December 2004 sourced by lava flowing from a crater formed in 1993 by a phreatic eruption. We measured the radiative heat flux from the two lakes in December 2004 using a compact infrared (IR) imaging camera. Daily thermal IR surveys from the Main Crater rim provide images of the lava lake surface temperatures and identify sites of upwelling and downwelling. The radiative heat outputs calculated for the Ray and Werner Lakes are 30–35 MW and 20 MW, respectively. We estimate that the magma flux needed to sustain the combined heat loss is ~ 250–710 kg s− 1, that the minimum volume of the magma reservoir is 2 km3, and that the radius of the conduit feeding the Ray lake is ~ 2 m.  相似文献   

2.
Strombolian eruptions from the long-lived lava lake of Erebus volcano, Ross Island, Antarctica, generate repeating Very Long Period (VLP) signals, containing energy between approximately 30 and 5 s, that persist for several minutes and through the post-eruptive refilling of the lava lake. The initial approximately 10 s of this signal is moderately variable, particularly with respect to its initial polarity, while the following VLP coda has been observed to be stable since the earliest VLP observations were made (1996). To estimate forces and force couples consistent with the Erebus VLP signature, we perform moment tensor inversions for point sources using high signal-to-noise data stacks from the six-station, 18-component broadband seismographic network and Green's function forward calculations that incorporate topography. We infer a shallow (approximate depth of less than 400 m below the lava lake surface) source centroid that underlies the center to the northwestern rim of the main crater, east and north of the lava lake. Integrated Mii functions over the predominant (180 s) signal duration of VLP events show that the net scalar moments for these events are on the order of 4 × 1013 N m (corresponding to a moment magnitude mw ≈ 3) for typical sized VLP events. Moment rate tensors which characterize force couple components are dominated (85–97% of variance) by dilatational components. Approximately 25% of the data variance is attributable to single forces that are attributable to oscillatory reaction forces caused by fluid transport, however, the relative contributions of vertical forces and couples with this sparse network is poorly resolved for these shallow sources. The generally high degree of repeatability in the VLP signal across thousands of eruptions over the past decade indicates that the response of the conduit system to gas slug ascent and subsequent gravitational disequilibrium is stable, consistent with the generally unchanging surface manifestation of the convecting lava lake system, and arguing for a thermally and dynamically stable conduit system beneath the lava lake.  相似文献   

3.
We invert for acoustic source volume outflux and momentum imparted to the atmosphere using an infrasonic network distributed about the erupting lava lake at Mount Erebus, Ross Island, Antarctica. By modeling these relatively simple eruptions as monopole point sources we estimate explosively ejected gas volumes that range from 1,000 m3 to 24,000 m3 for 312 lava lake eruptions recorded between January 6 and April 13, 2006. Though these volumes are compatible with bubble volumes at rupture (as estimated from explosion video records), departures from isotropic radiation are evident in the recorded acoustic wavefield for many eruptions. A point-source acoustic dipole component with arbitrary axis orientation and strength provides precise fit to the recorded infrasound. This dipole source axis, corresponding to the axis of inferred short-duration material jetting, varies significantly between events. Physical interpretation of dipole orientation as being indicative of eruptive directivity is corroborated by directional emissions of ejecta observed in Erebus eruption video footage. Although three azimuthally distributed stations are insufficient to fully characterize the eruptive acoustic source we speculate that a monopole with a minor amount of oriented dipole radiation may reasonably model the primary features of the recorded infrasound for these eruptions.  相似文献   

4.
Emission rates of sulfur dioxide (SO2) were measured at Erebus volcano, Antarctica in December between 1992 and 2005. Since 1992 SO2 emissions rates are normally distributed with a mean of 61 ± 27 Mg d− 1 (0.7 ± 0.3 kg s− 1) (n = 8064). The emission rates vary over minutes, hours, days and years. Hourly and daily variations often show systematic and cyclic trends. Long-wavelength, large amplitude trends appear related to lava lake area and both are likely controlled by processes occurring at depth. Time series analysis of continuous sequences of measurements obtained over periods of several hours reveals periodicity in SO2 output ranging from 10 to 360 min, with a 10 min cycle being the most dominant. Closed and open-system degassing models are considered to explain observed variable degassing rates. Closed-system degassing is possible as rheological stiffening and stick/slip may occur within the system. However, the timescales represented in these models do not fit observations made on Erebus. Open-system degassing and convection fits the observations collected as the presented models were developed for a system similar to Erebus in terms of degassing, eruptive activity and process repose time. We show that with the observed emission rate (0.71 kg s− 1) and a crystal content of 30%, magma will cool 65 °C to match observed heat fluxes; this cooling is sufficient enough to drive convection.  相似文献   

5.
A two-channel or split-window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of Lake Yugama on Kusatsu–Shirane volcano in Japan in order to measure the temperature of its crater lake. These temperature calculations were validated using lake water temperatures that were collected on the ground. Overall, the agreement between the temperatures calculated using the split-window method and ground truth is quite good, typically ± 1.5 °C for cloud-free images. Data from fieldwork undertaken in the summer of 2004 at Kusatsu–Shirane allow a comparison of ground-truth data with the radiant temperatures measured using ASTER imagery. Further images were analyzed of Ruapehu, Poás, Kawah Ijen, and Copahué volcanoes to acquire time-series of lake temperatures. A total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed. Results of the split-window algorithm applied to ASTER images are reliable for monitoring thermal changes in active volcanic lakes. These temperature data, when considered in conjunction with traditional volcano monitoring techniques, lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting.  相似文献   

6.
The ca. 8800 14C yrs BP Sulphur Creek lava flowed eastward 12 km from the Schriebers Meadow cinder cone into the Baker River valley, on the southeast flank of Mount Baker volcano. The compositionally-zoned basaltic to basaltic andesite lava entered, crossed and partially filled the 2-km-wide and > 100-m-deep early Holocene remnant of Glacial Lake Baker. The valley is now submerged beneath a reservoir, but seasonal drawdown permits study of the distal entrant lava. As a lava volume that may have been as much as 180 × 106 m3 entered the lake, the flow invaded the lacustrine sequence and extended to the opposite (east) side of the drowned Baker River valley. The volume and mobility of the lava can be attributed to a high flux rate, a prolonged eruption, or both. Basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular, with pervasive hackly or blocky fractures. Together with pseudopillow fractures, these features reflect fracturing normal to penetrative thermal fronts and quenching by water. A fine-grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma-water explosions. Although the structures closely resemble those developed in lava-ice contact environments, establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone. The lava also invaded the lacustrine sequence, forming varieties of peperite, including sills that are conformable within the invaded strata and resemble volcaniclastic breccias. The peperite is generally fragmental and clast- or matrix-supported; fine-grained and rounded fluidal margins occur locally. The lava formed a thickened subaqueous plug that, as the lake drained in the mid-Holocene, was exposed to erosion. The Baker River then cut a 52-m-deep gorge through the shattered, highly erodible basalt.  相似文献   

7.
Understanding the characteristics of volcanic thermal emissions and how they change with time is important for forecasting and monitoring volcanic activity and potential hazards. Satellite instruments view volcanic thermal features across the globe at various temporal and spatial resolutions. Thermal features that may be a precursor to a major eruption, or indicative of important changes in an on-going eruption can be subtle, making them challenging to reliably identify with satellite instruments. The goal of this study was to explore the limits of the types and magnitudes of thermal anomalies that could be detected using satellite thermal infrared (TIR) data. Specifically, the characterization of sub-pixel thermal features with a wide range of temperatures is considered using ASTER multispectral TIR data. First, theoretical calculations were made to define a “thermal mixing detection threshold” for ASTER, which quantifies the limits of ASTER's ability to resolve sub-pixel thermal mixing over a range of hot target temperatures and % pixel areas. Then, ASTER TIR data were used to model sub-pixel thermal features at the Yellowstone National Park geothermal area (hot spring pools with temperatures from 40 to 90 °C) and at Mount Erebus Volcano, Antarctica (an active lava lake with temperatures from 200 to 800 °C). Finally, various sources of uncertainty in sub-pixel thermal calculations were quantified for these empirical measurements, including pixel resampling, atmospheric correction, and background temperature and emissivity assumptions.  相似文献   

8.
Six new 40Ar/39Ar and three cosmogenic 36Cl age determinations provide new insight into the late Quaternary eruptive history of Erebus volcano. Anorthoclase from 3 lava flows on the caldera rim have 40Ar/39Ar ages of 23 ± 12, 81 ± 3 and 172 ± 10 ka (all uncertainties 2σ). The ages confirm the presence of a second, younger, superimposed caldera near the southwestern margin of the summit plateau and show that eruptive activity has occurred in the summit region for 77 ± 13 ka longer than previously thought. Trachyte from “Ice Station” on the eastern flank is 159 ± 2 ka, similar in age to those at Bomb Peak and Aurora Cliffs. The widespread occurrences of trachyte on the eastern flank of Erebus suggest a major previously unrecognized episode of trachytic volcanism. The trachyte lavas are chemically and isotopically distinct from alkaline lavas erupted contemporaneously in the summit region < 5 km away.  相似文献   

9.
Explosive degassing at Erebus Volcano produces infrasound that can be used to locate, characterize, and quantify eruptive activity from multiple vents. We use a three element distributed microphone network to pinpoint eruption sources and track the activity at the prominent vents through time. Eruptive mechanisms for both source types are analyzed in conjunction with the telemetered time-synced video imagery. We identify two commonly active vents corresponding to the large (often > 10-m diameter) bubble bursts at the free surface of a persistent phonolitic lava lake (‘Ray Lake’), and the less frequent ash-rich eruptions from a constricted vent (‘Active Vent’) located ∼ 80 m from the lava lake. During a 3-month study interval from 6 January to 13 April 2006 we identified and mapped more than 350 eruptive sources from the lava lake and 20 sources from the ash vent. Lava lake events are characterized by high-amplitude infrasonic transients that reflect rapid (less than a few s) acceleration and rupture of magma bubble films followed by an explosion of pressurized gases. Precise infrasonic localization of the lava lake events to accuracies of a few m indicates variable bubble source locations across a 40 by 50-m region spanning the lava lake. Spatial variability is corroborated by the video data. In contrast, degassing from the ash vent produces longer-duration (tens of s), lower amplitude transients that reflect diminished impulsivity and an extended degassing duration, features that are corroborated by video. Because infrasound networks can operate continuously in all weather conditions and during both diurnal and seasonal polar darkness, and are easily incorporated into automatic processing, they significantly contribute to the completeness and quantification of eruption catalogues for Erebus.  相似文献   

10.
El Chichón crater lake appeared immediately after the 1982 catastrophic eruption in a newly formed, 1-km wide, explosive crater. During the first 2 years after the eruption the lake transformed from hot and ultra-acidic caused by dissolution of magmatic gases, to a warm and less acidic lake due to a rapid “magmatic-to-hydrothermal transition” — input of hydrothermal fluids and oxidation of H2S to sulfate. Chemical composition of the lake water and other thermal fluids discharging in the crater, stable isotope composition (δD and δ18O) of lake water, gas condensates and thermal waters collected in 1995–2006 were used for the mass-balance calculations (Cl, SO4 and isotopic composition) of the thermal flux from the crater floor. The calculated fluxes of thermal fluid by different mass-balance approaches become of the same order of magnitude as those derived from the energy-budget model if values of 1.9 and 2 mmol/mol are taken for the catchment coefficient and the average H2S concentration in the hydrothermal vapors, respectively. The total heat power from the crater is estimated to be between 35 and 60 MW and the CO2 flux is not higher than 150 t/day or ~ 200 gm− 2 day− 1.  相似文献   

11.
Satellite remote sensing represents a mature technology for long-term monitoring of volcanic activity at Mount Erebus, either independently or as a complement to field instrumentation. Observations made on 4290 discrete occasions over a six year period by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) indicate that the radiant flux from the volcano's summit crater (and by inference, the lava lake contained therein), while variable on the time scale of days to weeks, has varied little on an inter-annual basis over this period. The average radiant flux from the lake during this time was 15 MW, with a maximum flux of 100 MW. Such heat flux time-series have been shown to act as a reliable proxy for general levels of activity at erupting volcanoes around the world, particularly when these time-series are of a long duration. The apparent stability of Erebus' power output is in marked contrast to fluxes observed at three other terrestrial volcanoes, Erta ‘Ale (Ethiopia), Nyiragongo (Democratic Republic of Congo) and Ambrym (Vanuatu), which, while also hosting active lava lakes, all exhibit much greater variability in radiant flux over the same period of time. The results presented in this paper are confluent with those obtained from geochemical considerations of the Erebus' degassing regime, and confirm that remarkably stable open-system volcanism appears to be characteristic of this long-active volcano.  相似文献   

12.
The summit cone of the Erebus volcano contains two craters. The Main crater is roughly circular (∼ 500 m diameter) and contains an active persistent phonolite lava lake ∼ 200 m below the summit rim. The Side Crater is adjacent to the southwestern rim of the Main Crater. It is a smaller spoon-shaped Crater (250–350 m diameter, 50–100 m deep) and is inactive. The floor of the Side Crater is covered by snow/ice, volcanic colluvium or weakly developed volcanic soil in geothermal areas (a.k.a. warm ground). But in several places the walls of the Side Crater provide extensive vertical exposure of rock which offers an insight into the recent eruptive history of Erebus. The deposits consist of lava flows with subordinate volcanoclastic lithologies. Four lithostratigraphic units are described: SC 1 is a compound lava with complex internal flow fabrics; SC 2 consists of interbedded vitric lavas, autoclastic and pyroclastic breccias; SC 3 is a thick sequence of thin lavas with minor autoclastic breccias; SC 4 is a pyroclastic fall deposit containing large scoriaceous lava bombs in a matrix composed primarily of juvenile lapilli-sized pyroclasts. Ash-sized pyroclasts from SC 4 consist of two morphologic types, spongy and blocky, indicating a mixed strombolian-phreatomagmatic origin. All of the deposits are phonolitic and contain anorthoclase feldspar.  相似文献   

13.
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14.
Ground surveys made during August, 1961, show large vertical magnetic intensity anomalies associated with the partly lava filled crater of Kilauea Iki. A vertical magnetic variation of 11,600 gammas occurs along a north-south profile across the crater, the maximum being on the north rim of the crater and the minimum on the south edge of the encrusted lava lake below the south rim. An east-west profile shows less vertical magnetic variation, with lake-surface measurements 1500 to 2500 gammas lower than measurements on the east rim of the crater. Computed anomalies using two-dimensional potential field graticules are in good agreement with the observed anomalies and support the following conclusions: 1) Average measured values of remanent magnetization of 10?2 cgs units and susceptibilities of 10?3 cgs units give reasonable magnitudes to the computed anomalies. 2) The remanent magnetization is parallel to the earth’s present magnetic field. 3) The maximum vertical magnetic field value in the north-south profile is the result of reinforcement of the positive terrain effect of the north rim of the crater and the positive edge effect of the north side of the lava lake. 4) The minimum value in the same profile is the result of reinforcement of the negative terrain effect at the base of the south rim of the crater and the negative edge effect of the south side of the lava lake. 5) Variation in the east-west magnetic profile is less because the terrain and edge effects of the horizontal components of the earth’s magnetic field and remanent magnetization approach zero. Changes in vertical magnetic field values as the lake solidifies will be maximum at the north edge of the lava lake, but more consistent changes of the opposite sign will occur on the south side of the lava lake. Total change will be approximately + 2300 gammas between the August 1961 measurement at station S6 and the value at that point when the entire lava lake has cooled below 400° C. The maximum rate of change at station S6 will occur when the 500° C isotherm is 35 to 65 meters below the surface and will be about 28 gammas per meter of lowering of the 500°C surface. Because of the steep magnetic anomalies associated with the lava lake and crater rims, the permanent magnetization presently forming in the cooling lake crust will have inclinations as much as 12° less than the average 37.5° inclination in the Kilauea area.  相似文献   

15.
We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May–July 2003 eruption at Piton de la Fournaise (La Réunion). Multiple oblique ground-based thermal images were merged to provide full coverage of the flow-field. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless, extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from 94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface that were 6–24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge Rate (TADR) ranged between 1.5 × 108 J m−3 and 3.5 × 108 J m−3. This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained from GPS surveys (Coppola et al. 2005). Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements, particularly in terms of calculating discharge rate trends.  相似文献   

16.
Volcanic emission rates of As, Sb, Pb, Hg, Se, Cl, and F were determined at Erebus volcano, Antarctica and White Island, New Zealand, using chemical traps. The trace metal fluxes were determined by combining the species to S ratios in the solutions with SO2 emission rates measured by correlation spectrometry at the two volcanoes. At Erebus volcano, fluxes for the metals Pb and Hg were 2.0 × 10− 4 and 8.1 × 10− 6 kg s− 11, respectively. Fluxes for Cl, F, As, Sb and Se (0.35, 0.15, 2.5 × 10− 4, 1.2 × 10− 5, and 4.5 × 10− 6 kg s− 1, respectively) agreed within error limits for values determined previously by the LiOH impregnated filter method [Zreda-Gostynska, G., Kyle, P., Finnegan, D., Prestbo, K., 1997. Volcanic gas emissions from Mount Erebus and their impact on the Antarctic environment. Journal of Geophysical Research, 102(B7): 15039–15055.], demonstrating the utility of the chemical trap method. A fall in the As/S ratio from 7 × 10− 4 in 1997/1999 to 3 × 10− 4 in 2000 at Erebus coincided with a change in the frequency and style of eruptive activity that may have been due to injection of magma into the system. At White Island, chemical trap data indicated fluxes of Cl = 0.90, F = 0.0079, Pb = 2.7 × 10− 4, Hg = 1.1 × 10− 5, As = 1.3 × 10− 4, Sb = 1.9 × 10− 5 and Se = 1.5 × 10− 5 kg s− 1. Samples collected 600 m downwind of the active crater were comparable to samples collected adjacent to the main gas vent, showing that this method can still be used at some distance from a degassing vent.  相似文献   

17.
Kaguyak Caldera lies in a remote corner of Katmai National Park, 375 km SW of Anchorage, Alaska. The 2.5-by-3-km caldera collapsed ~ 5.8 ± 0.2 ka (14C age) during emplacement of a radial apron of poorly pumiceous crystal-rich dacitic pyroclastic flows (61–67% SiO2). Proximal pumice-fall deposits are thin and sparsely preserved, but an oxidized coignimbrite ash is found as far as the Valley of Ten Thousand Smokes, 80 km southwest. Postcaldera events include filling the 150-m-deep caldera lake, emplacement of two intracaldera domes (61.5–64.5% SiO2), and phreatic ejection of lakefloor sediments onto the caldera rim. CO2 and H2S bubble up through the lake, weakly but widely. Geochemical analyses (n = 148), including pre-and post-caldera lavas (53–74% SiO2), define one of the lowest-K arc suites in Alaska. The precaldera edifice was not a stratocone but was, instead, nine contiguous but discrete clusters of lava domes, themselves stacks of rhyolite to basalt exogenous lobes and flows. Four extracaldera clusters are mid-to-late Pleistocene, but the other five are younger than 60 ka, were truncated by the collapse, and now make up the steep inner walls. The climactic ignimbrite was preceded by ~ 200 years by radial emplacement of a 100-m-thick sheet of block-rich glassy lava breccia (62–65.5% SiO2). Filling the notches between the truncated dome clusters, the breccia now makes up three segments of the steep caldera wall, which beheads gullies incised into the breccia deposit prior to caldera formation. They were probably shed by a large lava dome extruding where the lake is today.  相似文献   

18.
Heat and mass transfer rates were studied at the Niragongo lava lake during two expeditions directed by H. Tazieff in 1959 and 1972. The results of this study are as follows:Heat is transferred to the surface of the lake by the movement of lava; gas discharge is a result and not the cause of convection. The chemical composition of the gases and magma has changed very little between 1959 and 1972, whereas the mass and energy outputs differ by an order of magnitude. In 1977 a catastrophic explosion seems to have been caused by tectonic factors, stopping the slow convection of magma under the volcano and hence reducing surface manifestations in the form of the lava lake and escaping fumarolic and magmatic gases. The gas discharge was, in tons day−1, 5000 for H2O, 11,000 for CO2, 1000 for SO2 in 1959, and in 1972 7700 for H2O, 180,000 for CO2 and 23,000 for SO2. These values correspond to an energy transfer of 0.9 × 109 W in 1959 and 16 × 109 W in 1972.  相似文献   

19.
Between 1986 and 1990 the eruptive activity of Erebus volcano was monitored by a video camera with on-screen time code and recorded on video tape. Corresponding seismic and acoustic signals were recorded from a network of 6 geophones and 2 infrasonic microphones. Two hundred Strombolian explosions and three lava flows which were erupted from 7 vents were captured on video. In December 1986 the Strombolian eruptions ejected bombs and ash. In November 1987 large bubble-bursting Strombolian eruptions were observed. The bubbles burst when the bubble walls thinned to ∼ 20 cm. Explosions with bomb flight-times up to 14.5 s were accompanied by seismic signals with our local size estimate, “unified magnitudes” (mu), up to 2.3. Explosions in pools of lava formed by flows in the Inner Crater were comparatively weak.  相似文献   

20.
We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu, Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became centred. This is capped by a second package of thin (<45 cm thick) sheets of pahoehoe extending no more than 50 m from the channel. The upper-most package comprises localised ′a′a overflows. The channel itself contains two blockages located 130 m apart and composed of levee chunks veneered with overflow lava. The channel was emplaced over 50 h, spanning 30 May–2 June, 1974, with the flow front arriving at our section (4.4 km from the vent) 8 h after the eruption began. The basal ′a′a flow thickness yields effusion rates of 35 m3 s−1 for the opening phase, with the initial flow advancing across the mapped section at ∼10 m/min. Short-lived overflows of fluid pahoehoe then built the levee cap, increasing the apparent channel depth to 4.8 m. There were at least six pulses at 90–420 m3 s−1, causing overflow of limited extent lasting no more than 5 min. Brim-full flow conditions were thus extremely short-lived. During a dominant period of below-bank flow, flow depth was ∼2 m with an effusion rate of ∼35 m3 s−1, consistent with the mean output rate (obtained from the total flow bulk volume) of 23–54 m3 s−1. During pulses, levee chunks were plucked and floated down channel to form blockages. In a final low effusion rate phase, lava ponded behind the lower blockage to form a syn-channel pond that fed ′a′a overflow. After the end of the eruption the roofed-over pond continued to drain through the lower blockage, causing the roof to founder. Drainage emplaced inflated flows on the channel floor below the lower blockage for a further ∼10 h. The complex processes involved in levee–channel construction of this short-lived case show that care must be taken when using channel dimensions to infer flow dynamics. In our case, the full channel depth is not exposed. Instead the channel floor morphology reflects late stage pond filling and drainage rather than true channel-contained flow. Components of the compound levee relate to different flow regimes operating at different times during the eruption and associated with different effusion rates, flow dynamics and time scales. For example, although high effusion rate, brim-full flow was maintained for a small fraction of the channel lifetime, it emplaced a pile of pahoehoe overflow units that account for 60% of the total levee height. We show how time-varying volume flux is an important parameter in controlling channel construction dynamics. Because the complex history of lava delivery to a channel system is recorded by the final channel morphology, time-varying flow dynamics can be determined from the channel morphology. Developing methods for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable. We here achieve this by using high-resolution spatial data for a channel system at Kilauea. This study not only indicates those physical and dynamic characteristics that are typical for basaltic lava flows on Hawaiian volcanoes, but also a methodology that can be widely applied to effusive basaltic eruptions.  相似文献   

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