scholarly journals Earthquake Analysis Suggests Dyke Intrusion in 2019 Near Tarawera Volcano, New Zealand

2021 ◽  
Vol 8 ◽  
Author(s):  
Thomas W. Benson ◽  
Finnigan Illsley-Kemp ◽  
Hannah C. Elms ◽  
Ian J. Hamling ◽  
Martha K. Savage ◽  
...  
Keyword(s):  
New Zealand ◽  
Monitoring Network ◽  
Similar Process ◽  
Recent Event ◽  
Pyroclastic Deposits ◽  
Volcanic Event ◽  
Basaltic Composition ◽  
Lateral Distance ◽  
Magmatic Intrusions ◽  
Synthetic Models

Tarawera volcano (New Zealand) is volumetrically dominated by rhyolitic lavas and pyroclastic deposits, but the most recent event in AD 1886 was a basaltic Plinian fissure eruption. In March 2019 a swarm of at least 64 earthquakes occurred to the NE of Tarawera volcano, as recorded by the New Zealand Geohazard Monitoring Network (GeoNet). We use seismological analysis to show that this swarm was most likely caused by a dyke that intruded into the brittle crust between depths of 8–10 km and propagated toward Tarawera volcano for 2 km at a rate of 0.3–0.6 m s−1. We infer that this was a dyke of basaltic composition that was stress-guided toward Tarawera volcano by the topographic load of the volcanic edifice. Dyke intrusions of this nature are most likely a common occurrence but a similar process may have occurred during the 1886 eruption with a dyke sourced from some lateral distance away from the volcano. The 2019 intrusion was not detected by InSAR geodesy and we use synthetic models to show that geodetic monitoring could only detect a ≥6 m wide dyke at these depths. Improvements to geodetic monitoring, combined with detailed seismological analysis, could better detect future magmatic intrusions in the region and serve to help assess ongoing changes in the magmatic system and the associated possibilities of a volcanic event.

scholarly journals Seismic monitoring of the Auckland Volcanic Field during New Zealand's COVID-19 lock-down

2020 ◽  
Author(s):  
Kasper van Wijk ◽  
Calum J. Chamberlain ◽  
Thomas Lecocq ◽  
Koen Van Noten
Keyword(s):  
New Zealand ◽  
Seismic Noise ◽  
Template Matching ◽  
Monitoring Network ◽  
Volcanic Field ◽  
Local Network ◽  
Auckland Volcanic Field ◽  
Near Surface ◽  
Local Seismicity ◽  
The City

Abstract. The city of Auckland, New Zealand (Tamaki Makaurau, Aotearoa) sits on top of an active volcanic field. Seismic stations in and around the city monitor activity of the Auckland Volcanic Field (AVF), and provide data to image its subsurface. The seismic sensors – some positioned at the surface and others in boreholes – are generally noisier during the day than the night. For most stations weekdays are noisier than weekends, proving human activity contributes to recordings of seismic noise, even on seismographs as deep as 384 m below the surface, and as far as 15 km from Auckland's Central Business District. Lock-down measures in New Zealand to battle the spread of COVID-19 allow us to separate sources of seismic energy and evaluate both the quality of the monitoring network, as well as the level of local seismicity. A matched-filtering scheme based on template matching with known earthquakes improved the existing catalogue of 5 known local earthquakes to 35 for the period between November 1st, 2019 and June 15th, 2020. However, the Level 4 lock-down from March 25th to April 27th – with its drop in anthropogenic seismic noise – did not mark an enhanced detection level. Nevertheless, it may be that wind and ocean swell mask the presence of weak local seismicity, particularly near surface-mounted seismographs in the Hauraki Gulf that show much higher levels of noise than the rest of the local network.

scholarly journals Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

2017 ◽  
Vol 54 (6) ◽  
pp. 654-676 ◽  
Author(s):  
Kate E. Rubingh ◽  
Harold L. Gibson ◽  
Bruno Lafrance
Keyword(s):  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
Stratigraphic Correlation ◽  
Pyroclastic Deposits ◽  
Volcanic Event ◽  
Vms Deposits ◽  
Flin Flon ◽  
Arc Setting ◽  
Gold Producer ◽  
Back Arc

The thrust-bounded McLeod Road – Birch Lake (MB) sequence occurs within the Paleoproterozoic Snow Lake arc (SLA) assemblage of the Flin Flon belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust-bounded Chisel sequence indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km3). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the SLA. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz (43 699 kg) gold producer. The overlying MORB-like Birch Lake basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting. However, if they are thrust fault bounded, then they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust-bounded MB and SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.

scholarly journals Systematic revision of the trans-Bassian moriomorphine genus Theprisa Moore (Coleoptera, Carabidae)

ZooKeys ◽  
2021 ◽  
Vol 1044 ◽  
pp. 339-373
Author(s):  
James K. Liebherr ◽  
Nick Porch ◽  
Matthew Shaw ◽  
Bronte E. Sinclair ◽  
David R. Maddison
Keyword(s):  
New Zealand ◽  
Cladistic Analysis ◽  
Morphological Characters ◽  
Carabid Beetle ◽  
The Other ◽  
Recent Event ◽  
Systematic Revision ◽  
Natural Group ◽  
The Third ◽  
Initial Event

The Australian genus Theprisa Moore, 1963, is taxonomically revised to comprise five species, two newly described: Theprisa darlingtoni Liebherr & Porch, sp. nov. of Tasmania, and Theprisa otway Liebherr, Porch & Maddison, sp. nov. from the Otway Ranges, Victoria. Two previously described species, T. australis (Castelnau) and T. montana (Castelnau), are distributed in the mountains of Victoria. The third previously described species, T. convexa (Sloane) is found in Tasmania. A lectotype is designated for T. convexa because the various syntypes are ambiguously labelled. Cladistic analysis based on morphological characters establishes monophyly of Theprisa relative to the Australian genera Sitaphe Moore and Spherita Liebherr. This and a second clade of Australian genera (Pterogmus Sloane, Thayerella Baehr, and Neonomius Moore) do not form a natural group, but are cladistically interdigitated among two monophyletic New Zealand lineages (Tarastethus Sharp, and Trichopsida Larochelle and Larivière) suggesting substantial trans-Tasman diversification among these groups. Hypothesized relationships within Theprisa are consistent with two bouts of speciation involving the Bass Strait; an initial event establishing T. convexa as adelphotaxon to the other four species, and a more recent event establishing the sister species T. darlingtoni and T. montana. Geographic restriction of T. otway to the Otway Ranges is paralleled by Otway endemics in several other carabid beetle genera, as well as by endemics in numerous other terrestrial arthropod taxa. Whereas these numerous Otway endemics support the distinctive nature of the Otway Range fauna, their biogeographic relationships are extremely varied, illustrating that the Otways have accrued their distinctive biodiversity via various means.

scholarly journals Recently Discovered Thick Bentonite Bed Hosted by the Lithothamnium Limestones (Badenian) in the Polish Part of the Carpathian Foredeep: The Evidence for Volcanic Origin

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1417
Author(s):  
Katarzyna Górniak ◽  
Tadeusz Szydłak ◽  
Piotr Wyszomirski ◽  
Adam Gaweł ◽  
Małgorzata Niemiec
Keyword(s):  
Volcanic Glass ◽  
Pyroclastic Rock ◽  
Clay Material ◽  
Pyroclastic Deposits ◽  
Volcanic Origin ◽  
Volcanic Event ◽  
X Ray ◽  
Carpathian Foredeep ◽  
Diffraction Imaging ◽  
First Time

In this paper, we discuss the hypothesis on the volcanic origin of the precursor sediments for a thick (0.6 m) clay bed, hosted by the sequence of lithothamnium limestones of the Pińczów Formation. Combined X-ray powder diffraction, imaging methods (optical and electron microscopy), and chemical analysis were used to document the volcanic markers, which were preserved in the rock studied. The results obtained show that the clay bed discussed is bentonite in origin. This bentonite, which can be called Drugnia Rządowa bentonite, is composed almost entirely of montmorillonite with little admixtures of quartz and biotite. A small amount of calcite is present, but only in the top of the bed. Despite that, the bentonite contains nothing but clay material—it is a model example of entirely altered pyroclastic rock, which retains texture originally developed in volcanic glass fragments and reveals the preserved original features of the precursor fallout pyroclastic deposits (rhyolitic in character). The thick bentonite beds, discovered for the first time within the Badenian lithothamnium limestones of the Pińczów Formation, can be considered as a record of a violent, explosive volcanic event related to the closure of the Outer Carpathian basin and the development of the Carpathian Foredeep.

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