234 research outputs found
Recommended from our members
Seafloor deformation and forecasts of the April 2011 eruption at Axial Seamount
Axial Seamount is an active submarine volcano located at the intersection between the Cobb hotspot and the Juan de Fuca spreading centre in the northeast Pacific Ocean1, 2. The volcano has been closely monitored since it erupted in 1998 (refs 3, 4). Since then, Axial Seamount seemed to exhibit a similar inflation–deflation cycle to basaltic volcanoes on land and, on that basis, was expected to erupt again sometime before 2014 or 2020 (refs 5, 6). In April 2011 Axial Seamount erupted. Here we report continuous measurements of ocean bottom pressure that document the deflation–inflation cycle of Axial Seamount between 1998 and 2011. We find that the volcano inflation rate, caused by the intrusion of magma, gradually increased in the months leading up to the 2011 eruption. Sudden uplift occurred 40–55 min before the eruption onset, which we interpret as a precursor event. Based on our measurements of ground deformation through the entire eruption cycle at Axial Seamount, we suggest that another eruption could occur as early as 2018. We propose that the long-term eruptive cycle of Axial Seamount could be more predictable compared with its subaerial counterparts because the volcano receives a relatively steady supply of magma through the Cobb hotspot and because it is located on thin oceanic crust at a spreading plate boundary
Recommended from our members
Imaging of CO₂ bubble plumes above an erupting submarine volcano, NW Rota-1, Mariana Arc
NW Rota-1 is a submarine volcano in the Mariana volcanic arc located ~100 km north of Guam.
Underwater explosive eruptions driven by magmatic gases were first witnessed there in 2004 and continued
until at least 2010. During a March 2010 expedition, visual observations documented continuous but
variable eruptive activity at multiple vents at ~560 m depth. Some vents released CO₂ bubbles passively
and continuously, while others released CO₂ during stronger but intermittent explosive bursts. Plumes of
CO₂ bubbles in the water column over the volcano were imaged by an EM122 (12 kHz) multibeam sonar
system. Throughout the 2010 expedition numerous passes were made over the eruptive vents with the ship
to document the temporal variability of the bubble plumes and relate them to the eruptive activity on the
seafloor, as recorded by an in situ hydrophone and visual observations. Analysis of the EM122 midwater
data set shows: (1) bubble plumes were present on every pass over the summit and they rose 200-400 m
above the vents but dissolved before they reached the ocean surface, (2) bubble plume deflection direction
and distance correlate well with ocean current direction and velocity determined from the ship’s acoustic
doppler current profiler, (3) bubble plume heights and volumes were variable over time and correlate with
eruptive intensity as measured by the in situ hydrophone. This study shows that midwater multibeam sonar
data can be used to characterize the level of eruptive activity and its temporal variability at a shallow submarine
volcano with robust CO₂ output.Keywords: multibeam sonar, carbon dioxide degassing, submarine eruption, seamoun
Recommended from our members
Eruption of South Sarigan Seamount, Northern Mariana Islands: Insights into Hazards from Submarine Volcanic Eruptions
The eruption of South Sarigan Seamount in the southern Mariana arc
in May 2010 is a reminder of how little we know about the hazards associated with
submarine explosive eruptions or how to predict these types of eruptions. Monitored
by local seismometers and distant hydrophones, the eruption from ~ 200 m water
depth produced a gas and ash plume that breached the sea surface and rose ~ 12 km
into the atmosphere. This is one of the first instances for which a wide range of pre- and
post-eruption observations allow characterization of such an event on a shallow
submarine volcanic arc volcano. Comparison of bathymetric surveys before and after
the eruptions of the South Sarigan Seamount reveals the eruption produced a 350 m
diameter crater, deeply breached on the west side, and a broad apron downslope with
deposits > 50 m thick. The breached summit crater formed within a pre-eruption
dome-shaped summit composed of andesite lavas. Dives with the Japan Agency for
Marine-Earth Science and Technology Hyper-Dolphin remotely operated vehicle
sampled the wall of the crater and the downslope deposits, which consist of andesite
lava blocks lying on pumiceous gravel and sand. Chemical analyses show that the
andesite pumice is probably juvenile material from the eruption. The unexpected
eruption of this seamount, one of many poorly studied shallow seamounts of
comparable size along the Mariana and other volcanic arcs, underscores our lack of
understanding of submarine hazards associated with submarine volcanism
Recommended from our members
Repeat bathymetric surveys at 1-metre resolution of lava flows erupted at Axial Seamount in April 2011
At sites with frequent submarine volcanic activity, it is difficult to discern between new and pre-existing lava flows. In particular, the distribution of the fissures from which lava erupts, the routes taken by lava flows and the relationship between the new flows and the pre-existing seafloor bathymetry are often unclear. The volcanic and hydrothermal systems of Axial Seamount submarine volcano in the Pacific Ocean have been studied intensively since eruptions were detected in 1998 (refs 1, 2) and 2011 (ref. 3). Here we combine pre- and post-eruption bathymetric surveys³⁻⁸ with 1-m lateral resolution and 0.2-m vertical precision, to precisely map the extent and thickness of the lava flows, calculate the volume of lava and unambiguously identify eruptive fissures from the April 2011 eruption. Where the new lava flows extend beyond the boundaries of the repeated surveys, we use shipboard multibeam surveys to map the flows with lower resolution. We show that the eruption produced both sheet and lobate flows associated with high eruption rates and low-eruption-rate pillow mounds. We find that lava flows erupted from new as well as existing fissures and tended to reoccupy existing flow channels. This reoccupation makes it difficult to map submarine flows produced during one eruption without before-and-after bathymetric surveys.Keywords: tectonics and geodynamics, Volcanology, Structural geology, mineralogy and petrolog
Recommended from our members
Volcanic Eruptions in the Deep Sea
Volcanic eruptions are important events in Earth’s cycle of magma generation and crustal construction. Over durations of hours to years, eruptions produce new deposits of lava and/or fragmentary ejecta, transfer heat and magmatic volatiles from Earth’s interior to the overlying air or seawater, and significantly modify the landscape and perturb local ecosystems. Today and through most of geological history, the greatest number and volume of volcanic eruptions on Earth have occurred in the deep ocean along mid-ocean ridges, near subduction zones, on oceanic plateaus, and on thousands of mid-plate seamounts. However, deep-sea eruptions (> 500 m depth) are much more difficult to detect and observe than subaerial eruptions, so comparatively little is known about them. Great strides have been made in eruption detection, response speed, and observational detail since the first recognition of a deep submarine eruption at a mid-ocean ridge 25 years ago. Studies of ongoing or recent deep submarine eruptions reveal information about their sizes, durations, frequencies, styles, and environmental impacts. Ultimately, magma formation and accumulation in the upper mantle and crust, plus local tectonic stress fields, dictate when, where, and how often submarine eruptions occur, whereas eruption depth, magma composition, conditions of volatile segregation, and tectonic setting determine submarine eruption style.Keywords: East Pacific rise,
Galapagos rift,
Axial volcano,
Mid-Atlantic ridge,
Lava-flow morphology,
Fuca ridge,
Northern cleft segment,
Hydrothermal activity,
Midocean ridg
Recommended from our members
Geologic history of the summit of Axial Seamount, Juan de Fuca Ridge
Multibeam (1 m resolution) and side scan data collected from an autonomous underwater vehicle, and
lava samples, radiocarbon-dated sediment cores, and observations of flow contacts collected by remotely
operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on
Axial Seamount’s summit and upper rift zones. The maps show 52 post-410 CE lava flows and 20
precaldera lava flows as old as 31.2 kyr, the inferred age of the caldera. Clastic deposits 1–2 m thick
accumulated on the rims postcaldera. Between 31 ka and 410 CE, there are no known lava flows near the
summit. The oldest postcaldera lava (410 CE) is a pillow cone SE of the caldera. Two flows erupted on
the W rim between ~800 and 1000 CE. From 1220 to 1300 CE, generally small eruptions of plagioclase
phyric, depleted, mafic lava occurred in the central caldera and on the east rim. Larger post-1400 CE
eruptions produced inflated lobate flows of aphyric, less-depleted, and less mafic lava on the upper rift
zones and in the N and S caldera. All caldera floor lava flows, and most uppermost rift zone flows,
postdate 1220 CE. Activity shifted from the central caldera to the upper S rift outside the caldera, to the N rift and caldera floor, and then to the S caldera and uppermost S rift, where two historical eruptions
occurred in 1998 and 2011. The average recurrence interval deduced from the flows erupted over the last
800 years is statistically identical to the 13 year interval between historical eruptions.Keywords: Lava flows, Juan de Fuca Ridge, Geologic, Mapping, Axial Seamoun
Recommended from our members
Eruptive modes and hiatus of volcanism at West Mata seamount, NE Lau basin: 1996–2012
We present multiple lines of evidence for years to decade-long changes in the location and
character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus
in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were
observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones
moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing
of seven multibeam bathymetric surveys of the volcano made in the 1996–2012 period reveals a pattern
of extended constructional volcanism on the summit and northwest flank punctuated by eruptions
along the volcano’s WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during
the observational period occurred between May 2010 and November 2011 at ~2920 m depth near the
base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during
the 1996–2012 period. The cessation of summit volcanism recorded on the moored hydrophone was
accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank.
Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a
remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on
the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be
as young as several thousand years.Keywords: Multibeam, Volcano, Submarine, Lau, Seamount, Eruptio
Recommended from our members
Submarine Magmatic-Hydrothermal Systems at the Monowai Volcanic Centre, Kermadec Arc
Authors listed on this Accepted Manuscript vary slightly from those listed on the Version of Record. Harold L. Gibson is an additional author on the published version.The Monowai volcanic centre (MVC) is located at the mid-point along the ~2530 km long Tonga-Kermadec arc system, is probably the most hydrothermally active submarine volcanic system globally. The MVC is comprised of a large elongate caldera (Monowai caldera, 7.9 x 5.7 km; 35 km²; depth to caldera floor is 1590 m), which has formed within an older caldera some 84 km² in area. To the south of the nested caldera system is a large composite volcano, Monowai cone, which rises to within ~ 100 m of the sea surface and has been volcanically active for at least several decades. Despite the large size, mafic volcanic rocks dominate the MVC; basalts are the most common rock type recovered; less common are basaltic andesites and andesites. Hydrothermal plume mapping during the 2004 NZAPLUME III cruise showed at least three major hydrothermal systems associated with the caldera and cone. Monowai cone has hydrothermal venting from the summit. This summit plume is gas-rich and acidic; plume samples show a pH shift of -2.00 pH units, δ³He up to 358 ‰, H₂S concentrations up to 32 μM and CH₄ concentrations up to 900 nM. The summit plume is also metal-rich with elevated total dissolvable Fe (TDFe up to 4200 nM), TDMn (up to 412 nM), and TDFe/TDMn (up to 20.4). Monowai caldera has a major hydrothermal vent system with plumes extending from ~ 1000 to 1400 m depth. The caldera plume has lower values for TDFe, although ranges to higher TDMn concentrations than the summit plume, and is relatively gas-poor (no H₂S detected, pH shift of -0.06 pH units, CH₄ concentrations up to 26 nM). Hydrothermal vents have been observed associated with prominent basaltic andesite ridges (Mussel Ridge) proximal to the southwest wall of the caldera (1025 – 1171 m depth). However, the composition of the hydrothermal plumes in the caldera are different to the vents, indicating that the source of the caldera plumes is at greater depth and is more metal-rich and therefore likely higher temperature. Minor plumes detected as light scattering anomalies down the northern flank of Monowai caldera most likely represent resuspension of volcanic debris. Particulate samples from both the cone sites and the caldera site are enriched in Al, Ti, Ca, Mg, Si, and S, with the cone summit plume especially enriched in K, As, W and Cu, Pb, Zn. The elevated Ti and Al suggest acidic water-rock reactions and intense high-sulfidation alteration of the host volcanic rocks. Observations from submersible dives with Pisces V in 2005 and the remotely operated vehicle ROPOS in 2007 of Mussel Ridge indicate numerous low temperature vents (< 60°C), with a large biomass of vent-associated fauna, in particular large accumulations of the mussel Bathymodiolus sp. and the tubeworm Lamellibrachia sp. We interpret the Monowai volcanic centre as possessing a robust high-sulfidation magmatic-hydrothermal system, with significant differences in the style and composition of venting at the cone and caldera sites. At Monowai cone, the large shifts in pH, elevated TDFe and TDFe/TDMn, and H₂S-, CH₄- and ³He-rich nature of the plume fluids coupled with elevated Ti, P, V, S and Al in the particulates indicates significant magmatic volatile ± metal contributions to the hydrothermal system and aggressive acidic water-rock interaction. By contrast, Monowai caldera has low TDFe/TDMn in hydrothermal plumes; however, end-member vent fluid compositions, combined with presence of alunite, sulfide minerals and native sulfur in samples from Mussel Ridge suggest recent acid volatile-rich venting and active Fe-sulfide formation in the subsurface, and the potential for the presence of significant SMS mineralization
Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan
This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good
Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation
One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced.
Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI
- …