Formation of submarine flat-topped volcanic cones in Hawai'i

Lunar volcanic domes are essential windows into the local magmatic activities on the Moon. Classification of domes is a useful way to figure out the relationship between dome appearances and formation processes. Previous studies of dome classification were manually or semi-automatically carried out either qualitatively or quantitively. We applied an unsupervised machine-learning method to domes that are annularly or radially distributed around Gardner, a unique central-vent volcano located in the northern part of the Mare Tranquillitatis. High-resolution lunar imaging and spectral data were used to extract morphometric and spectral properties of domes in both the Gardner volcano and its surrounding region in the Mare Tranquillitatis. An integrated robust Fuzzy C-Means clustering algorithm was performed on 120 combinations of five morphometric (diameter, area, height, surface volume, and slope) and two elemental features (FeO and TiO2 contents) to find the optimum combination. Rheological features of domes and their dike formation parameters were calculated for dome-forming lava explanations. Results show that diameter, area, surface volume, and slope are the selected optimum features for dome clustering. 54 studied domes can be grouped into four dome clusters (DC1 to DC4). DC1 domes are relatively small, steep, and close to the Gardner volcano, with forming lavas of high viscosities and low effusion rates, representing the latest Eratosthenian dome formation stage of the Gardner volcano. Domes of DC2 to DC4 are relatively large, smooth, and widely distributed, with forming lavas of low viscosities and high effusion rates, representing magmatic activities varying from Imbrian to Eratosthenian in the northern Mare Tranquillitatis. The integrated algorithm provides a new and independent way to figure out the representative properties of lunar domes and helps us further clarify the relationship between dome clusters and local magma activities of the Moon.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 2: Predicted emplacement processes and observations)

High‐resolution bathymetry and side‐scan data of the Vance, President Jackson, and Taney near‐ridge seamount chains in the northeast Pacific were collected with a hull‐mounted 30‐kHz sonar. The central volcanoes in each chain consist of truncated cone‐shaped volcanoes with steep sides and nearly flat tops. Several areas are characterized by frequent small eruptions that result in disorganized volcanic regions with numerous small cones and volcanic ridges but no organized truncated conical structure. Several volcanoes are crosscut by ridge‐parallel faults, showing that they formed within 30–40 km of the ridge axis where ridge‐parallel faulting is still active. Magmas that built the volcanoes were probably transported through the crust along active ridge‐parallel faults. The volcanoes range in volume from 11 to 187 km3, and most have one or more multiple craters and calderas that modify their summits and flanks. The craters (<1 km diameter) and calderas (>1 km diameter) range from small pit craters to calderas as large as 6.5×8.5 km, although most are 2–4 km across. Crosscutting relationships commonly show a sequence of calderas stepping toward the ridge axis. The calderas overlie crustal magma chambers at least as large as those that underlie Kilauea and Mauna Loa Volcanoes in Hawaii, perhaps 4–5 km in diameter and ∼1–3 km below the surface. The nearly flat tops of many of the volcanoes have remnants of centrally located summit shields, suggesting that their flat tops did not form from eruptions along circumferential ring faults but instead form by filling and overflowing of earlier large calderas. The lavas retain their primitive character by residing in such chambers for only short time periods prior to eruption. Stored magmas are withdrawn, probably as dikes intruded into the adjacent ocean crust along active ridge‐parallel faults, triggering caldera collapse, or solidified before the next batch of magma is intruded into the volcano, probably 1000–10,000 years later. The chains are oriented parallel to subaxial asthenospheric flow rather than absolute or relative plate motion vectors. The subaxial asthenospheric flow model yields rates of volcanic migration of 3.4, 3.3 and 5.9 cm yr−1 for the Vance, President Jackson, and Taney Seamounts, respectively. The modeled lifespans of the individual volcanoes in the three chains vary from 75 to 95 kyr. These lifespans, coupled with the geologic observations based on the bathymetry, allow us to construct models of magma supply through time for the volcanoes in the three chains.

Low elevation flank eruptions represent highly hazardous events due to their location near, or in, communities. Their potentially high effusion rates can feed fast moving lava flows that enter populated areas with little time for warning or evacuation, as was the case at Nyiragongo in 1977. The January–March 1974 eruption on the western flank of Mount Etna, Italy, was a low elevation effusive event, but with low effusion rates. It consisted of two eruptive phases, separated by 23 days of quiescence, and produced two lava flow fields. We describe the different properties of the two lava flow fields through structural and morphological analyses using UAV-based photogrammetry, plus textural and rheological analyses of samples. Phase I produced lower density (∼2,210 kg m−3) and crystallinity (∼37%) lavas at higher eruption temperatures (∼1,080°C), forming thinner (2–3 m) flow units with less-well-developed channels than Phase II. Although Phase II involved an identical source magma, it had higher densities (∼2,425 kg m−3) and crystallinities (∼40%), and lower eruption temperatures (∼1,030°C), forming thicker (5 m) flow units with well-formed channels. These contrasting properties were associated with distinct rheologies, Phase I lavas having lower viscosities (∼103 Pa s) than Phase II (∼105 Pa s). Effusion rates were higher during Phase I (≥5 m3/s), but the episodic, short-lived nature of each lava flow emplacement event meant that flows were volume-limited and short (≤1.5 km). Phase II effusion rates were lower (≤4 m3/s), but sustained effusion led to flow units that could still extend 1.3 km, although volume limits resulted from levee failure and flow avulsion to form new channels high in the lava flow system. We present a petrologically-based model whereby a similar magma fed both phases, but slower ascent during Phase II may have led to greater degrees of degassing resulting in higher cooling-induced densities and crystallinities, as well as lower temperatures. We thus define a low effusion rate end-member scenario for low elevation effusive events, revealing that such events are not necessarily of high effusion rate and velocity, as in the catastrophic event scenarios of Etna 1669 or Kilauea 2018.

Mount Etna is an open conduit volcano, characterised by persistent activity, consisting of degassing and explosive phenomena at summit craters, frequent flank eruptions, and more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which represent the greatest hazard by the volcano to the inhabited areas. Historical documents and scientific papers related to the 20th century effusive activity have been examined in detail, and volcanological parameters have been compiled in a database. The cumulative curve of emitted lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval, characterised by a moderate slope of the curve, amounting to 436 × 106 m3 of lava with average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase in eruption frequency is associated with a large issued lava volume (767 × 106 m3) and a higher effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have been further subdivided into two categories: eruptions characterised by high effusion rates and short duration, and eruptions dominated by low effusion rate, long duration and larger volume of erupted lava. Circular zones around the summit area have been drawn for summit eruptions based on the maximum lava flow length; flank eruptions have been considered by taking into account the eruptive fracture elevation and combining them with lava flow lengths of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south and east sectors of the volcano. This should be properly considered in future land-use planning by local authorities.

Statistical analysis of the historical activity of Mount Etna, aimed at the evaluation of volcanic hazard

Mayotte 2018 eruption likely sourced from a magmatic mush

Research Article| February 01, 1970 Diapiric Structures on the Campeche Shelf and Slope, Western Gulf of Mexico J ALAN BALLARD; J ALAN BALLARD Global Ocean Floor Analysis and Research (Project), U.S. Naval Oceanographic Office, Washington, D.C. 20390 Search for other works by this author on: GSW Google Scholar ROBERT H FEDEN ROBERT H FEDEN Global Ocean Floor Analysis and Research (Project), U.S. Naval Oceanographic Office, Washington, D.C. 20390 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (2): 505–512. https://doi.org/10.1130/0016-7606(1970)81[505:DSOTCS]2.0.CO;2 Article history received: 30 Jun 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J ALAN BALLARD, ROBERT H FEDEN; Diapiric Structures on the Campeche Shelf and Slope, Western Gulf of Mexico. GSA Bulletin 1970;; 81 (2): 505–512. doi: https://doi.org/10.1130/0016-7606(1970)81[505:DSOTCS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Recently collected seismic reflection profiles reveal numerous emerged and buried diapiric structures along the Campeche Shelf and slope, south of 20° N. latitude. Slope diapirs have steep sides, relatively flat tops, and a subsurface reflector which may be an expression of caprock. Shelf diapirs are buried structures characterized by uniformly stratified sediments trapped between rising intrusives or displaced by numerous high-angle faults.The limited east-west distribution and the lack of magnetic signature suggest that Campeche Sheli and slope diapirs are salt structures co-linear with previously mapped salt domes in the Tabasco-Campeche Basin and the Sigsbee Knolls. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A short phonon pulse injected into liquid $^{4}\text{H}\text{e}$ propagates away from the heater as a phonon sheet. The angular dependence of the energy flux has a mesa shape, i.e., a flat top, which is the phonon sheet, and steep sides. The mesa shape is caused by high energy phonon creation in the pulse along the symmetry axis; this depletes energy from the flux until the central portion of the pulse has a constant energy. The low energy phonons then occupy a thin sheetlike volume. We have measured the width of the phonon sheet from three heaters of different widths at different heater powers and distances from the heater. We find the remarkable result that the sheet width is inversely proportional to the width of the rectangular heater. Also the height of the mesa falls off as the inverse square of the distance from the heater. We present a phenomenological model for the phonon propagation in liquid helium at 0 bar, which predicts these dependencies. It also predicts that the sheet width is proportional to the heater pulse length, and is only a weak function of heater power, both of which are seen experimentally.

Beam-shaping plays a very important role in the field of laser processing. Laser quench needs a rectangular speckle, which has a flat top, steep sides, high efficiency and low sidelobes. Diffractive phase elements (DPEs) have many superexcellent characters, which conventional optical elements have difficulties to achieve. Designing of the phase plane comes down to phase retrieval problem. Geometrical transformation and multiform iterative algorithms, such as G-S algorithm, Input-Output algorithm, ST algorithm are adopted. Through comparison of the results from different methods, some evaluations about algorithms are made. ST algorithm is the most feasible method for the problem, the result of which can meet the requirements of practical process. Some simulation experiments and discussions about algorithms have been done. To be fabricated as a binary optical element (BOE), the result of design has been quantified to 16 steps.

Gravity and magnetic anomalies off the west coast of the North Island are caused by igneous bodies much larger than any observed on land in New Zealand. North of Auckland the bodies resemble seamounts in shape and size; they appear to be volcanic piles about 5-6 km thick with steep sides and flat tops which form the sea floor, and are surrounded by sediments. South of Auckland the anomalies can only be interpreted as due to composite bodies. The greater parts of the gravity anomalies are probably due to igneous material intruding Tertiary sediments; the greater parts of the magnetic anomalies are probably due to igneous rocks intruding late Paleozoic basement. Unlike the northern anomalies which occur as isolated features, the southern anomalies lie on an extensive zone of magnetic activity which may run into the Norfolk Ridge. The relationship of the offshore bodies to the much smaller onshore volcanic features is by no means clear, but it would appear that the coastline separates regions of quite different tectonic styles.

Summary The Bouguer anomaly map of the Isle of Man is dominated by two gravity lows, elongated in a north-east to south-west direction across the island, and by a rapid decrease of values at the Point of Ayre. The two anomalies are thought to be due to granite bodies, here named the South Barrule and Glen Mona granites, intruded into the Manx Group, and these granites are inter­preted as having broad, flat tops and steep sides, those of the South Barrule Granite reaching a depth of ten kilometres. The Manx Group in the vicinity of these anomalies contains mineral lodes and granite apophyses. The steep gradients in the area of the Point of Ayre are thought to be due to the Permo-Triassic sediments which form part of the southern edge of the Solway Firth basin. The cause of a gravity high near Jurby in the northern plain is unclear, but a rock-unit of high density underlying the Manx Group may be responsible.

Axially symmetrical diffractive phase planes (DPPs) are easily fabricated and have been used in a variety of applications, especially for realizing uniform loop focal spot with steep side, flat top, flat side lobe and high efficiency. A kind of hybrid design algorithm combined ST algorithm and input-output algorithm is introduced for axially symmetrical DPPs design to realize uniform loop focal spot. The computer simulation has shown that the algorithm is robust and convergent. The DPPs has been designed to product uniform loop focal spot with high diffractive efficiency of the energy inside the loop spot, high uniformity for both main lobe and side lobe (both more than 96%), and steep side simultaneously.

The acidic flows from Serra Geral Formation in Torres Syncline, Rio Grande do Sul, Brazil, are on the top of a volcanic sequence composed by a complex facies association of compound, simple and rubbly pahoehoebasic flows, acidic lava domes, and tabular acidic lava flows. The origin and emplacement conditions of the acidic volcanic rocks are discussed in this paper based on petrology, on calculated apatite saturation thermometry temperatures, and on estimated viscosity data. The liquidus temperatures for metaluminous rhyodacite to rhyolite samples are about 1,067.5 ± 25oC in average. The viscosity (η) values vary from 105 to 106 Pas for anhydrous conditions, suggesting the emplacement of high-temperature - low-viscosity lava flows and domes. The occurrence of acidic lava domes above simple pahoehoe flows as flow-banded vitrophyres was under low effusion rates, in spite of their high temperature and low viscosities, which are reflected in their small height. The emplacement of lava domes has continued until the eruption of rubbly pahoehoe flows and the geometry of these deposits rugged the relief. Presence of tabular acidic lava flows covering the landscape indicates that it was under high effusion rates conditions and such flows had well-insulated cooled surface crusts. The capacity to attain greater distances and overpass relief obstacles is explained not only by high effusion rates, but also by very low viscosities at the time of emplacement.

The Early Cretaceous Ontong Java Plateau (OJP) in the western equatorial Pacific, Earth's most voluminous large igneous province (LIP), is characterized by intrabasement seismic reflections. To investigate the nature of such reflections, we have analyzed new and all older multichannel seismic (MCS) reflection data from the OJP using an instantaneous phase velocity analysis technique and synthetic seismograms. Intrabasement reflections are most prevalent on the main OJP, especially on its crest. On MCS data, the reflections (1) are semicontinuous and subparallel to the top of igneous basement; (2) in places, have the opposite phase of seafloor reflections; and (3) have an average frequency of ∼20 Hz. We calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at OJP scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the MCS data. Alternatively, to evaluate the possibility of sediment/sedimentary rock interbeds causing the intrabasement reflections, we use published Early Cretaceous sedimentation rates determined from OJP drill sites and published estimates for the duration of massive OJP volcanism to calculate a range of possible sedimentary interbed thicknesses. The range proves to be below the detection limit of the MCS data. Therefore, we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates, both originating from vents and fissures on the OJP, probably on its crest.