Active Volcanic Belt Research Articles

Magmatic origins and storage conditions for the historic eruption of Tseax Volcano, British Columbia, Canada

The Northern Cordilleran Volcanic Province (NCVP) is the most active volcanic belt in Canada, yet there are few detailed petrologic studies of the individual volcanoes. Tseax volcano is the southernmost volcanic centre of the NCVP, the second youngest (~1700 CE) eruption in Canada, and led to one of Canada's worst natural disasters killing up to ~2000 Nisga'a First Nation people. We present a conceptual model for the origins, evolution and pre-eruptive storage of the Tseax magma which erupted in ~0.5 km3 of volcanic material, mainly in the form of valley-filling lava flows. All Tseax products are alkali Fe- Ti- rich basanite-to-tephrite having trace element distributions similar to the other mafic NCVP lavas. Phenocrysts consist of plagioclase, olivine and titanomagnetite, often forming glomerocrysts suggesting co-crystallisation of these 3 mineral phases. Clinopyroxene is never observed as a phenocryst phase. The lavas have low Mg#’s implying they are fractionated relative to a mantle-derived ‘parent’ magma. Trace elements indicate the magma derives from melting of a fertile mantle source (i.e., (Nb/K)n ~ 1), most likely the upper asthenosphere. There is no evidence in the Tseax volcanic rocks for magma mixing or lithospheric contamination during ascent. The phenocryst assemblage suggests rapid ascent of a low viscosity magma to <5.5 km where titanomagnetite becomes the first phase on the liquidus (~ 1133 °C). There the magma stalled for a very short period of time under PT conditions where clinopyroxene did not reach saturation. Based on the size of the plagioclase phenocrysts, the magma stalled for less than a year and cooled down to 1094–1087 °C prior to eruption.

Permian sedimentary tuff tight reservoirs in the Santanghu Basin, NW China

Sedimentary tuffs comprise important tight oil reservoirs in the Middle Permian Tiaohu Formation in the Santanghu Basin. This paper describes three research advances made on these reservoirs. (1) There are many sets of sedimentary tuff in the second member of the Tiaohu Formation and they are the “sweet section” for tight oil exploration. Vitric, crystal-vitric, and argillaceous tuffs are the main reservoir types, of which the first two are more favorable. (2) A model was established to show how the volcanic edifice controls the type and distribution of the volcanic lacustrine tuff deposition. The crystal-vitric tuff is distributed in the lacustrine deposits nearest to the volcanic crater, and the vitric tuff is distributed on both sides of the active volcanic belt a certain distance from the crater, and this is the most favorable distribution area for sedimentary tuff. Later devitrification resulted in formation of a large number of micro-pores, and this is the main reason for the presence of favorable reservoirs. (3) The sedimentary tuff reservoir has undergone successive geological processes from formation of secondary dissolution pores, then hydrocarbon charge and accumulation, to compaction. The tight oil accumulation is the result of the coupling of the diagenetic evolution of the tuff in the Tiaohu Formation and the hydrocarbon generation and charging from the shale in the Lucaogou Formation.

Magma Fracking Beneath Active Volcanoes Based on Seismic Data and Hydrothermal Activity Observations

Active volcanoes are associated with microearthquake (MEQ) hypocenters that form plane-oriented cluster distributions. These are faults delineating a magma injection system of dykes and sills. The Frac-Digger program was used to track fracking faults in the Kamchatka active volcanic belt and fore-arc region of Russia. In the case of magma laterally injected from volcanoes into adjacent structures, high-temperature hydrothermal systems arise, for example at Mutnovsky and Koryaksky volcanoes. Thermal features adjacent to these active volcanoes respond to magma injection events by degassing CO2 and by transient temperature changes. Geysers created by CO2-gaslift activity in silicic volcanism areas also flag magma and CO2 recharge and redistributions, for example at the Uzon-Geyserny, Kamchatka, Russia and Yellowstone, USA magma hydrothermal systems. Seismogenic faults in the Kamchatka fore-arc region are indicators of geofluid fracking; those faults can be traced down to 250 km depth, which is within the subduction slab below primary magma sources.

The Increasing Severity of Circumpacific Natural Disasters

The Ring of Fire guards the margins of the continents and island arcs bordering the Pacific Ocean. Active volcanic belts dominate the terrestrial landscape, and about 100 km offshore, oceanic trenches parallel the volcanoes. This topographically rugged, geologically unstable transition separating subaerial and submerged portions of the solid Earth is a reflection of convergent and transform lithospheric plate boundaries. The plates themselves are carried along by thermally driven mantle convection. Slow but inexorable differential motions along the plate junctions are responsible for the globe's most intense seismic activity as well as deadly eruptions. Tsunamis, avalanches, mudflows, and catastrophic land subsidence are common associates in this dynamic geologic realm. Moreover, the world's greatest ocean—a heat—transfer engine driven convectively by incoming solar radiation—spawns the most powerful tropical storms, producing devastating coastal flooding. Nowhere is the Pacific Rim free of these natural hazards. As the burgeoning populations of the Circumpacific nations occupy and more intensively develop and degrade ever—larger tracts along the Rim, the aggregate vulnerability of society to natural hazards will increase. To the extent that these same Circumpacific nations increasingly influence global economic systems, the cascade of suffering produced by episodic natural disasters and the rapid transmission of communicable diseases inevitably will produce more substantial financial as well as human and material losses. We can mitigate but not eliminate the adverse effects of natural hazards through a more complete understanding of their fundamental scientific causes, and by planning accordingly. But natural disaster reduction must be coordinated across and transcend political boundaries if we are to be more effective in the future.

Geothermal systems in Iceland: Structure and conceptual models—II. Low-temperature areas

A review and assessment of data pertaining to the origin and nature of low-temperature geothermal activity in Iceland are presented. This activity is widely distributed in Quaternary and Tertiary formations on the American plate in western Iceland west of the active belts of volcanism and rifting but it is very sparse on the European plate east of these belts. Low-temperature systems occur in a few places within the active volcanic belts. Temperatures range from just above ambient to a little over 150°C. Generally speaking, resevoir temperatures decrease with increasing distance from the active volcanic belts. The distribution of the low-temperature areas can be correlated to a large extent with active tectonism. In Iceland the European plate is tectonically stable but in the American plate the shear stress field is complicated, leading to complex fracturing and faulting of the crust at present. No single generalized conceptual model describes the basic features of all low-temperature areas in Iceland. Low-temperature geothermal activity is considered to develop by one of the following four processes, or any combination of them: (1) deep flow of groundwater from highland to lowland areas through permeable structures driven by the hydraulic gradient; (2) convection in young fractures formed by tectonic movements in old and relatively impermeable bedrock; (3) drift of high-temperature geothermal systems out of the active volcanic belts in conjunction with their cooling and extinction of the magma heat source; and (4) magma intrusion into Quaternary or Tertiary formations adjacent to the active volcanic belts. Formation of permeable fractures by recent earth movements is probably the most common process responsible for the development of low-temperature activity through convection in these fractures. Convection in low-temperature systems with temperatures above some 60°C is probably mostly driven by pressure differences created by a relatively light hot water column within the system and a denser cold water column outside it. In systems of lower temperature the convection is driven by hydrostatic head in the recharge areas. The source of the low-temperature waters is largely meteoric. However, in some coastal areas a significant seawater-groundwater component is present, up to 10%. Waters not containing a seawater component are low in dissolved solids, or in the range 150–500 ppm. The reason is the low content of anions, particularly Cl, in the basaltic rock forming soluble salts with the major aqueous cations. Geothermal waters from the low-temperature areas in Iceland typically possess lower δD-values (more negative) than the local precipitation. This difference is variable; most often it lies in the range of 10–30% δD, but it may be as large as 70‰. This difference has been considered to indicate that the recharge areas to the low-temperature areas lie inland on higher ground, the distance being as much as 150 km. The interpretation favoured here is that at least some of the low-temperature waters contain a component of “ice-age water”, i.e. water that is older than about 10, 000 years. The “ice-age water” is depleted in deuterium relative to today's precipitation. When “ice-age water” is present in the geothermal water, deuterium cannot be used as a tracer to locate the recharge areas to the geothermal areas and in this way to deduce about regional groundwater flow.

Geothermal systems in Iceland: Structure and conceptual models—I. High-temperature areas

There are 20 known high-temperature geothermal areas in Iceland and another eight potential areas. Surface manifestations are meagre in these eight areas and not conclusive, and no drilling has been carried out to prove or disprove the existence of high-temperature geothermal systems at depth. The high-temperature areas are located within the active volcanic belts or marginal to them. The heat source is considered to be magmatic, shallow level crustal magma chambers in the case of high-temperature systems associated with central volcanic complexes, but dyke swarms for the systems on the Reykjanes Peninsula where no central volcanoes have developed. Fossil high-temperature systems are abundant in Quaternary and Tertiary formations as witnessed by alteration of the basaltic eruptive rocks into lower-greenschist mineral assemblages. The fossil systems are typically associated with central volcanoes where intrusives account for 50% or more of the rock. The fossil systems are considered to have formed within the active volcanic belts but drifted out of them in conjunction with crustal accretion within these belts. In the process they may develop into low-temperature geothermal systems. Permeability is very variable within the drilled high-temperature areas, in the range 1–150 millidarcies. The best permeability generally appears to be associated with sub-vertical fractures and faults. Permeability is poorest when the reservoir rock consists dominantly of intrusives, such as at Krafla, northeastern Iceland. It appears that intrusives are most abundant in reservoirs associated with central complexes that have developed a caldera. Temperatures follow the boiling point curve with depth, at least to the level of the deepest wells, in some areas, but in others they are lower. The highest recorded downhole temperature is >380°C. Hydrological considerations and permeability data favour that convection is density driven and that the source water is shallow groundwater in the vicinity of these systems. This groundwater is in most cases of meteoric origin. However, in three areas on the Reykjanes Peninsula it is largely or solely marine. The deuterium content of geothermal waters of meteoric origin is often lower than that of local precipitation. This has been taken to indicate that the source of supply is precipitation that has fallen on higher ground inland. This may indeed be the case, but flow from the source area is considered to be shallow. In some cases the low δD-values may stem from the presence of a component of an old water, which is isotopically lighter than today's precipitation at any particular site because the climate in Iceland was colder in the past. The geothermal seawater at Reykjanes and Svartsengi, southwestern Iceland, is considerably lower in deuterium than seawater. The cause of this is not known. However, reaction between seawater and basaltic rocks at very low temperatures may contribute, as well as rising of H 2 gas from deep levels and its reaction at shallower levels in the geothermal system to form water, but H 2 gas is much more depleted in deuterium than the associated water. Degassing of the magma heat source appears to add chemical constituents to the geothermal waters, such as boron, carbon and sulphur. Sometimes there may also be addition of Cl and H 2O during events of recharge of new magma into the magma chambers in the roots of the geothermal system such as has been observed in the Krafla area. The high-temperature geothermal waters are close to chemical equilibrium with alteration minerals for all major components, except Cl and B. The alteration minerals typically display depth zoning because many of them are stable only over a limited temperature range. At temperatures above about 250°C the alteration mineral assemblage is that of the greenschist metamorphic facies. Precipitation of carbon as calcite and sulphur as sulphides, where boiling occurs in upflow zones of high-temperature geothermal systems, leads to strong enrichment of carbon and sulphur in the altered rock.

Processes controlling the distribution of boron and chlorine in natural waters in Iceland

The concentrations of B and Cl in natural waters in Iceland lie in the range 0.001–10 and 1–20,000 ppm, respectively. Lowest concentrations occur in surface and groundwaters in the central highlands. Highest Cl concentrations are found in high-temperature waters on the Reykjanes Peninsula and highest B concentrations in well waters from high-temperature geothermal systems in the axial zones of the active volcanic belts. The B and Cl contents of Icelandic basalts are 0.1–6.6 and 75–750 ppm, respectively. These large variations are considered to result from variable degassing during consolidation as well as concentration variations in the initial magma. Tholeftes are lowest in both elements (av. 1.2 ppm B and 170 ppm CI), transitional basalts intermediate (av. 2.1 ppm B and 240 ppm CI), and alkali-basalts highest (av. 3.8 ppm B and 340 ppm Cl). Cl B ratios in tholeiites are most often within 25–50, but somewhat lower in alkali basalts. Most geothermal waters contain B and Cl within 0.05–1 and 10–100 ppm, respectively. These rather low values are attributed to the low content of B and Cl in the basaltic rock. The B and Cl distribution in the Icelandic natural waters indicate that these elements act as essentially incompatible. Their sources of supply include (1) the atmosphere (seawater spray and aerosols), (2) the rock with which the water interacts, (3) seawater-groundwater, and (4) magma intrusions. In surface water and nonthermal groundwater the dominant source of supply of Cl is seawater spray and aerosols, but the soil and rock contribute often significantly to the B in these waters. Their Cl B ratio is similar to that of seawater (1330) or somewhat lower. Boron and Cl concentrations generally increase with water temperature. Warm waters (<50°C) usually possess Cl B ratios intermediate between those of seawater and basalt. With increasing temperature this ratio decreases and gradually approaches that of the rock. Some high-temperature geothermal waters have as low Cl B ratios as 1 and B concentrations as high as 10 ppm. The cause is either B degassing of the magmatic intrusive heat source or phase separation in the producing aquifer. Some low-temperature waters (<150°C) in low lying areas by the coast have elevated Cl concentrations due to the presence of a component of seawater-groundwater that entered the bedrock during the deglaciation period when the lowland areas were submerged. Estimation of the marine component of Cl in waters of the low-temperature systems that do not contain a seawater-groundwater component indicate that the recharge is most often local, but not distantly derived from elevated areas inland as has been inferred from their deuterium content.

Eruptions in Space and Time: Durations, Intervals, and Comparison of World's Active Volcanic Belts: ABSTRACT

A computerized data bank, compiled over the last 12 years at the Smithsonian Institution, allows summaries to be made of Holocene volcanism. The Scientific Event Alert Network tracks current volcanic activity. However, the record of most volcanoes is poor before the last 100 years, and some eruptions still pass unreported. The time interval since the previous eruption can be calculated for 4835 of the 5564 compiled eruptions. The median interval is 5.0 years, but much longer intervals commonly precede unusually violent eruptions. For the 25 most violent eruptions in the file (with known preceding interval), the medium interval is 865 years. Of the historic eruptions in this group, 50% resulted in fatalities. The interval between an eruption's start and its most violent paroxysm may be measured in months or years, but it is usually short. Of the 205 larger eruptions for which data are available, 92 had the paroxysmal event within the first day of the eruption, allowing little time for emergency preparations after the eruption's opening phase. To compare the recent vigor of different volcanic belts, they calculated the number of years in which each volcano was active in the last 100 years, summed these for each belt, andmore » divided by belt length. Another index of recent vigor is the number of recognized Holocene volcanoes divided by belt length. A third index is the number of large explosive eruptions (volcanic explosive index greater than or equal to 3) of the last 100 years, again normalized by belt length. These three measures correlate reasonably well, serving to contrast vigorous belts such as Kamchatka, Central America, and Java with relatively quiet belts such as the Cascades, South Sandwich Islands, Greece, and southern Chile.« less

Geothermal energy potential related to active volcanism in Indonesia

About 90 thermal areas in Indonesia are indicated, most of which could be grouped into hyperthermal areas located in active volcanic belts. The thermal manifestations are fumaroles, geysers, hot springs and hot mud-pools with surface temperatures generally at boiling point or more than 70°C. A tentative evaluation has been made of the potential of 54 thermal areas with a view to their further development for electrical power. The successful results of these studies in several thermal areas suggest that these volcanic geothermal systems have a high energy potential of about 13,000 – 14,000 MW. The Kawah Kamojang geothermal field in West Jawa is the first promising attempt at utilizing this geothermal energy for electrical power; a 30 MW geothermal power plant has already been installed, and a further 3 units totalling 165 MW are planned.

Gravity field around Japan — sea gravimetry by the Geological Survey of Japan

Abstract Using a LaCoste & Romberg sea gravimeter, more than 60,000 gravity measurements were obtained from 11 research cruises around Japan, as conducted by the Geological Survey of Japan from 1974 to 1979. From the misties∗ of free‐air anomalies the r.m.s. accuracy of the measurements was estimated to be 2.8 mgal (with the satellite navigation system and an EM‐log) and 0.7 mgal (with a Doppler sonar system). From this result it was suggested that the observed gravity error was mainly due to the ship's velocity measurements. Mean free‐air anomalies of 15’ × 15’, 30’ × 30’, and 1° × 1° were calculated using these measurements and compared with the previous data A free‐air anomaly map in the area of 22°N to 46°N and 123°E to 148°E was compiled based mainly on these data. The map fully covers four island arc and trench systems—the Northeast Japan, the Ogasawara (Bonin), the Southwest Japan, and the Ryukyu Arc and Trench—and they are associated with paired belts of large‐amplitude positive and negative anomalies. There are broad positive anomaly belts landward of the trenches, which are due to the high‐density subducting Iithospheric slabs. Seaward of the active volcanic belts, belts of large‐amplitude positive anomalies are observed. The basement in these areas seems to be uplifted, and the crust has a higher mean density. Negative anomalies are observed at the margins of the Japan Basin and the Yamato Basin. These anomalies are due to the edge effect of the roots of the neighboring continental or subcontinental crust. Isostatic anomalies in these basins are probably almost constant.

Strontium isotope evidence for petrogenesis of Central American andesites

THE active volcanic belts of Mexico and of Central America can be considered in two groups (Fig. 1). The Mexican volcanic belt (MVB) forms an irregular line trending away from the Middle America Trench, running from Ceboruco and Colima in the west to San Martin on the Caribbean coast1. In contrast to the MBV, the active Central American volcanic belt runs some 1,200 km from southern Mexico (Tacana) and Guatemala to Costa Rica, broadly parallel with the Middle America Trench1. With the exception of the alkaline volcano San Martin2, these are all calc-alkaline andesite volcanoes1. Between Mexico and El Salvador, the volcanic chain is built on a crust which includes Precambrian and Lower Palaeozoic crystalline rocks3,4. Southeast of El Salvador, in Nicaragua and Costa Rica the crust is composed mainly of Cainozoic volcanic and sedimentary rocks resting on Cretaceous ultramafic complexes3–6. This change in basement character does not seem to be reflected in the composition of volcanic rocks7. Here we report new Sr isotope data for Cainozoic volcanic rocks from Costa Rica, and by comparing these with earlier published data we conclude that all of these volcanic rocks have their origin in the mantle and that a sialic contribution to their origin is insignificant.

Geothermal heat flow in the North Island of New Zealand

Abstract The heat flow at 23 sites in the North Island of New Zealand was deduced from the geothermal gradients measured in drillholes and the thermal conductivities of the rocks penetrated. The flow is below normal to the south-east and above normal to the north-west of the active volcanic belt. Within and near this belt, zero geothermal gradients were measured, although the combined heat flow from the hydrothermal fields is known to be equivalent to a mean heat flow 20 times the normal value for the whole belt. The hydrothermal fields are regarded as narrow upflow zones in convectively circulated meteoric water systems. The zero geothermal gradients suggest that a large part of the whole volcanic belt and some areas immediately west of it provide the intake for these convective systems.