James White | University of Otago (original) (raw)

Papers by James White

The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lac... more The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre-and post-eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption. Here we examine the volcanic ash produced during the August eruption with the aim of determining whether juvenile magma was erupted or not. The widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results. The Te Maari ash sorting and trend towards a unimodal grain-size distribution increase with distance along the dispersal axis. Proximal to intermediate sites showing polymodal grain-size distributions can be related to the refragmentation of different pre-existing lithologies, overlapped erupted pulses and transport mechanisms, and to particle aggregation. Between 69 and 100 vol.% of particles coarser than 3 ϕ and 45-75 vol.% of grains finer than 3 ϕ were sourced from the pre-existing, commonly hydrothermally altered, vent-area lavas and pyroclasts. Free crystals (pyroxene N plagioclase N magnetite N pyrite) make up 0-23 vol.% of particles coarser than 3 ϕ, and 22-41 vol.% of grains finer than 3 ϕ. Brown to black fragments of fresh glass are a small (1-15 vol.%), but notable, component. Under SEM, these blocky, glassy particles are poorly vesicular, and irregularly shaped, some with fluidal or bubble-wall surfaces, and others with fragmented stepped surfaces and fine adhering ash. In thin section, they contain variable amounts of microlites within an isotropic groundmass. The range in silica content of the microprobe-analysed glass is very wide (56-77 wt.%) and cannot be correlated to any specific particle textural type. These chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts; both their diversity, and their match with vent country rocks, argue strongly against a "juvenile" origin for the glassy fragments. We conclude that rising magma provided only heat and gas into the overlying, sealed vapour-dominated hydrothermal system. A landslide from this area led to a rapid decompression and ash was produced by top-down hydrothermal explosions. Careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations, as well as to the context of their source vent, in order to be confident that new magma has reached the surface.

The dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of ... more The dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of the simplest volcanic plumbing systems. Their geometry is controlled by interaction of magma-driven cracks with country rock, and reveals regional structural and stress patterns at the time of their emplacement. The shallow stress field, however, may change during the time an intrusion complex is emplaced, in response to addition or removal of magma and country rock during associated surface eruptions. The Jagged Rocks Complex, in the Miocene Hopi Buttes Volcanic Field, Navajo Nation, Arizona, is exposed 300–350 m below the pre-eruptive surface. It comprises a group of generally NW–SE striking dikes, punctuated in places by buds, a saucer-like intrusion, larger pyroclastic massifs and a diatreme. We made measurements of 13 dikes, divided into 172 segments, with thicknesses from 8 to 122 cm (mean 43 cm) and lengths of 60 to 780 m. Several sills and inclined sheets in places are thicker than dikes, having mean thicknesses of 48 cm and 73 cm respectively. Dikes typically show straight, parallel, and en echelon patterns, while sills and inclined sheets are curved. The northwestern dikes differ from the rest in containing large mafic crystals, and are inferred to have been emplaced after the others. We find that the strike of the overall complex (dikes and other sheets, elongate massifs and aligned sub-cylindrical bodies) reflects a crystalline-basement control that is evident throughout Hopi Buttes. Over the period of the complex's emplace-ment, local stress patterns were not stable. We infer that excavation of deep maar craters, and perhaps the construction of a scoria cone at the surface, modified the local stress patterns to favor emplacement of sills and en echelon dikes later in the complex's evolution, in contrast to simple straight dikes as the complex first formed.

Geological Society of America Bulletin, 2012

... was used to understand how the break in erup-tive activity and vent migration may have been r... more ... was used to understand how the break in erup-tive activity and vent migration may have been related to changes in magma composition and possible transitions between separate pulses of alkali basaltic magma, as has been postulated for other Jeju volcanoes (Brenna et al ...

Journal of Volcanology and Geothermal Research, 2014

Journal of the Geological Society, 2003

Individual volcanoes of continental monogenetic volcanic fields are generally presumed to erupt s... more Individual volcanoes of continental monogenetic volcanic fields are generally presumed to erupt single magma batches during brief eruptions. Nevertheless, in two unrelated volcanic fields (the Waipiata volcanic field, New Zealand, and the Miocene-Pliocene volcanic field in western Hungary), we have identified pronounced and systematic compositional differences among products of individual volcanoes. We infer that this indicates a two-stage process of magma supply for these volcanoes. Each volcano records: (1) intrusion of a basanitic parent magma to lower-to mid-crustal levels and its subsequent fractionation to form a tephritic residual melt; (2) subsequent transection of this reservoir by a second batch of basanitic melt, with tephrite rising to the surface at the head of the propagating basanite dyke. Eruption at the surface then yields initial tephrite, typically erupted as pyroclasts, followed by eruption and shallow intrusion of basanite from deeper in the dyke. By analogy with similar tephrite-basanite eruptions along rift zones of intraplate ocean-island volcanoes, we infer that fractionation to tephrite would have required decades to centuries. We conclude that the two studied continental monogenetic volcanic fields demonstrate a consistent history of early magmatic injections that fail to reach the surface, followed by capture and partial eruption of their evolved residues in the course of separate and significantly later injections of basanite that extend to the surface and erupt. This systematic behaviour probably reflects the difficulty of bringing small volumes of dense, primitive magma to the surface from mantle source regions. Ascent through continental crust is aided by the presence in the dyke head of buoyant tephrite captured during transection of the earlier-emplaced melt bodies.

Journal of Volcanology and Geothermal Research, 2008

Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, the... more Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material,

Bulletin of Volcanology, 2008

In diatremes and other volcanic vents, steep bodies of volcaniclastic material having differing p... more In diatremes and other volcanic vents, steep bodies of volcaniclastic material having differing properties (particle size distribution, proportion of lithic fragments, etc.) from those of the surrounding vent-filling volcaniclastic material are often found. It has been proposed that cylindrical or cone-shaped bodies result from the passage of "debris jets" generated after phreatomagmatic explosions or other discrete subterranean bursts. To learn more about such phenomena, we model experimentally the injection of gas-particulate dispersions through other particles. Analogue materials (glass beads or sand) and a finite amount of compressed air are used in the laboratory. The gas is made available by rapidly opening a valvetherefore the injection of gas and coloured particles into a granular host is a brief (<1 s), discrete event, comparable to what occurs in nature following subterranean explosions. The injection assumes a bubble shape while expanding and propagating upwards. In reaction, the upper part of the clastic host moves upward and outward above the 'bubble', forming a 'dome'. The doming effect is much more pronounced for shallow injection depths (thin hosts), with dome angles reaching more than 45°. Significant surface doming is also observed for some full-scale subterranean blasts (e.g. buried nuclear explosions), so it is not an artefact of our setup. What happens next in the experiments depends on the depth of injection and the nature of the host material. With shallow injection into a permeable host (glass beads), the compressed air in the "bubble' is able to diffuse rapidly through the roof. Meanwhile the coloured beads sediment into the transient cavity, which is also closing laterally because of inward-directed granular flow of the host. Depending on the initial gas pressure in the reservoir, the two-phase flow can "erupt" or not; non-erupting injections produce cylindrical bodies of coloured beads whereas erupting runs produce flaring upward or conical deposits. Changing the particle size of the host glass beads does not have a large effect under the size range investigated (100-200 to 300-400 µm). Doubling the host thickness (injection depth) requires a doubling of the initial gas pressure to produce similar phenomena. Such injections -whether erupting or wholly subterranean -provide a compelling explanation for the origin and characteristics of multiple cross-cutting bodies that have been documented for diatreme and other vent deposits.

Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatrem... more Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in

ABSTRACT When a magmatic melt encounters water, heat is transferred and in many cases the melt is... more ABSTRACT When a magmatic melt encounters water, heat is transferred and in many cases the melt is fragmented to varying degrees by a range of processes. Explosive MFCI interactions result from extremely rapid heat transfer during fine fragmentation. Under other conditions, interactions extend from quiet steaming to non- explosive granulation. Among the many variables in natural environments inferred to play a role in determining the style of magma-water interaction is the presence of impurities, such as particulate sediment, in the water. This has been argued to be of particular significance for interactions within volcanic vents, where debris accumulates during the course of an eruption. A simple set of experiments was undertaken at the Physical Volcanology Lab in Wuerzburg, Germany, to investigate the effect of such particulate mixtures. Magma (~200 gm) was poured from a fixed height into a receptacle with pure water, and water with 10, 20, and 30 percent suspended mud. Thermocouple and force measurements were collected during and after each pour, and reveal that with increasing sediment concentrations, the rate of heat transfer from magma to coolant, and the intensity of thermal granulation, is progressively reduced. The scale of reduction is impressive; for water, virtually all heat transfer from magma to water is complete within a few seconds after the pour, whereas with 30 percent suspended clay this stretches to in excess of 10 minutes. The change reflects reduced fragmentation of the magma, reduced heat capacity of the coolant, and strongly reduced convection in the coolant. A separate pour into a liquefied sand-clay sediment (64 percent sediment by mass) produced similarly reduced heat transfer, but was accompanied by quiet but pervasive hydrodynamic fragmentation of the melt into centimetric glass spheres, many of which welded together within the sediment.

Geological Society of …, Jan 1, 2012

Field observations and structural data from intrusive complexes at Allan Hills and Terra Cotta Mo... more Field observations and structural data from intrusive complexes at Allan Hills and Terra Cotta Mountain, South Victoria Land, Antarctica, demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface. These sills and sheets represent the upper-crustal (top 4 km) plumbing system of the 183 Ma Ferrar large igneous province. The sheets are short in length (<1500 m), are moderately inclined
(47° and 51° means), and show meter-scale variations in attitude; in places, they intruded bedding planes, resulting in stepped sheet-sill geometries. Sheet geometries and their relationship to the surrounding country rock are consistent with peripheral sheet intrusion under local magmatic stresses arising from roof-lift during sill injection. The sheet intrusions thus reflect the intrusive process itself rather than a far-field tectonic stress regime. The sills and sheets, together with local dolerite masses, formed the intrusive network that supplied magma to the Mawson Formation pyroclastic rocks in various parts of South Victoria Land and, by inference, the Kirkpatrick flood basalt lavas. The predominance of inclined sheets rather than steeply dipping dikes indicates a magmatic environment that is unlike the Jurassic rift arm inferred by previous authors. This could be explained using any of the following three scenarios. (1) The axis of the rift, and hence any rift-hosted dikes, lies beyond the current exposure area. (2) The regionally extensive Ferrar sills may have provided rheologically weak horizons that limited mechanical coupling of the basement rocks and overlying Beacon Supergroup, locally detaching the upper 4 km of the crust from possible synmagmatic basement extension below. (3) TheFerrar large igneous province was emplaced in a neutral tectonic setting. In this scenario, broad-scale distribution of magma through the province was controlled by preexisting structure in the basement, and local intrusion geometries refl ect the physical interaction of intruding magma with bedding anisotropy of the Beacon Supergroup.

Geophysical Journal …, Jan 1, 2012

We analyse 10 representative intrusions from two sets of inclined diabase (Ferrar Dolerite) sheet... more We analyse 10 representative intrusions from two sets of inclined diabase (Ferrar Dolerite) sheets exposed at Allan Hills (South Victoria Land, Antarctica), using petrographic and rock magnetic methods to determine microfabrics and infer magma flow directions. At least one diabase sample was collected at the margins of each intrusion. Magnetite and pyrrhotite contribute to magnetic fabrics of the samples. Thirty-six magnetic fabric directions, inferred from the mutual arrangement of either the magnetic lineation, or the magnetic foliation plane and local macroscopic flow indicators (e.g. horn-shaped apophyses and kinks) at the tips and margins of each intrusion reveal composite (i.e. both lateral and vertical) flow paths recorded along each intrusive segment. Petrographic textures and multiple flow directions inferred at sheet-segment tips reveal that ‘passive’ injection of magma via hydrofracturing produced the local shallowlarge igneous province plumbing as a sill-dominated intrusive complex very close to, or intersecting the palaeosurface. This contrasts with ‘classic’ arrays of either vertically or
laterally injected blade-like dykes.

Although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic... more Although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic eruptions, increasing recognition of volumetrically significant sill complexes suggests that they too play an important role in magma ascent through the shallow crust. However, the extent to which sills and interconnected, sill-fed dikes actually transport magma to the earth's surface in many large igneous provinces (LIP) is presently unclear. By analyzing field relationships and dimensions of intrusions of the Ferrar LIP in South Victoria Land, Antarctica, we show that sill-fed dikes were the likely feeders for voluminous flood basalt eruptions. These intrusions are small but numerous, with cumulative dimensions equivalent to a feeder network 308,000 km long and 1.8 m wide. Due to the tremendous aerial extent of this intrusive network, each individual dike-feeder segment would only be required to actively feed magma for 2 to 3 days on average to erupt the 70,000 km3 of flood lavas represented by the Kirkpatrick basalts. The Ferrar intrusions form a broadly-distributed array of small, moderately dipping dikes (<2 km long, 1.8 m wide, 56° mean dip) exhibiting almost any orientation. This sill-fed dike network contrasts with dike swarms conventionally depicted to feed flood basalt provinces, and has the appearance of a variably “cracked lid” atop a sill complex. The cracked lid model may apply to a range of shallow feeder systems (<4 km depth) intruding sedimentary basins, where the effects of far-field tectonic stresses are negligible and sill intrusions exert the dominant control on dike orientations. We conclude that sill inflation, and resulting deformation of surrounding host rock, plays a critical role in the ascent of magma in shallow volcanic systems that span the full spectrum of eruptive volumes.

Antarctic Science- …, Jan 1, 2011

Allan Hills nunatak, south Victoria Land, Antarctica, exposes an exceptional example of a shallow... more Allan Hills nunatak, south Victoria Land, Antarctica, exposes an exceptional example of a shallow depth (,500 m) intrusive complex formed during the evolution of the Ferrar large igneous province (LIP). Dyke distribution, geometries and relationships allow reconstruction of its history and mechanics of intrusion. Sills interconnect across host sedimentary layers, and a swarm of parallel inclined dolerite sheets is intersected by a radiating dyke-array associated with remnants of a phreatomagmatic vent, where the dolerite is locally quenched and mixed to form peperite. Intrusion geometries, and lack of dominant rift-related structures in the country rock indicate that magma overpressure, local stresses between mutually interacting dykes and vertical variations of host rock mechanical properties controlled the intrusive process throughout the thick and otherwise undeformed pile of sedimentary rocks (Victoria Group). Dolerite sills connected to one another by inclined sheets are inferred to record the preferred mode of propagation for magma-carrying cracks that represent the shallow portions of the Ferrar LIP plumbing system.

Although monogenetic volcanic fields pose hazards to major cities worldwide, their shallow magma ... more Although monogenetic volcanic fields pose hazards to major cities worldwide, their shallow magma feeders (<500 m depth) are rarely exposed and, therefore, poorly understood. Here, we investigate exposures of dikes and sills in the Hopi Buttes volcanic field, Arizona, to shed light on the nature of its magma feeder system. Shallow exposures reveal a transition zone between intrusion and eruption within 350 m of the syn-eruptive surface. Using a combination of field-and satellite-based observations, we have identified three types of shallow magma systems: (1) dike-dominated, (2) sill-dominated , and (3) interconnected dike-sill networks. Analysis of vent alignments using the pyroclastic massifs and other erup-tive centers (e.g., maar-diatremes) shows a NW-SE trend, parallel to that of dikes in the region. We therefore infer that dikes fed many of the eruptions. Dikes are also observed in places transforming to transgressive (ramping) sills. Estimates of the observable volume of dikes (maximum volume of 1.90 × 10 6 m 3) and sills (minimum volume of 8.47 × 10 5 m 3) in this study reveal that sills at Hopi Buttes make up at least 30 % of the shallow intruded volume (∼2.75 × 10 6 m 3 total) within 350 m of the paeosurface. We have also identified saucer-shaped sills, which are not traditionally associated with monogenetic volcanic fields. Our study demonstrates that shallow feeders in monogenetic fields can form geometrically complex networks, particularly those intruding poorly consolidated sedimentary rocks. We conclude that the Hopi Buttes eruptions were primarily fed by NW-SE-striking dikes. However, saucer-shaped sills also played an important role in modulating eruptions by transporting magma toward and away from eruptive conduits. Sill development could have been accompanied by surface uplifts on the order of decime-ters. We infer that the characteristic feeder systems described here for the Hopi Buttes may underlie monogenetic fields elsewhere, particularly where magma intersects shallow, and often weak, sedimentary rocks. Results from this study support growing evidence of the important role of shallow sills in active monogenetic fields.

Summer NS, Ayalon A (1995) Dike intrusion into unconsolidated sandstone and the development of qu... more Summer NS, Ayalon A (1995) Dike intrusion into unconsolidated sandstone and the development of quartzite contact zones. J Struct Geol 17:997-1010 Zimmermann K (1909) Die Absonderung des Sandsteines in Sa¨ulen und Prismen. Mitteil Nordbo¨hm Exkursions-Klubs 32:330-334 Analog modeling of the formation of wrinkles on the upper surface of saucer-shaped sill intrusions

Journal of Volcanology and Geothermal Research, 2003

The Miocene Waipiata Volcanic Field, New Zealand, is an eroded phreatomagmatic intracontinental v... more The Miocene Waipiata Volcanic Field, New Zealand, is an eroded phreatomagmatic intracontinental volcanic field formed during a period of weak lithospheric extension. The field includes remnants of at least 55 volcanoes in an area of V5000 km 2 . Vent-filling deposits comprising predominantly lava (e.g. plugs, necks, lava flows, or dykes), often associated with thin basal phreatomagmatic pyroclastic deposits, were classified as type 1 vents and are inferred to be the remnants of scoria cones. Vents represented by predominantly pyroclastic infill are classified as type 2 vents and are inferred to have been the substructures of phreatomagmatic tuff ring and/or maar volcanoes. Type 3 vent complexes are groups of closely spaced or overlapping vents, with voluminous preserved lava flows; they are inferred to be the remnants of volcanoes comprising adjoining to coalescing maars and tuff rings with magmatic explosive and effusive products. Pyroclastic rocks of most of the Waipiata vents record initial phreatomagmatic explosive activity fuelled by groundwater, followed by strombolian-style eruptions. Aligned and clustered vents are accommodated to structural features of the regional basement rock (Otago Schist). ß

Journal of Geophysical …, 2000

The 1949 rift zone eruption along the Cumbre Vieja ridge on La Palma involved three eruptive cent... more The 1949 rift zone eruption along the Cumbre Vieja ridge on La Palma involved three eruptive centers, 3 km spaced apart, and was chemically and mineralogically zoned. Duraznero crater erupted tephrite for 14 days and shut down upon the opening of Llano del Banco, a fissure that issued first tephrite and, after 3 days, basanite. Hoyo Negro crater opened 4 days later and erupted basanite, tephrite, and phonotephrite, while Llano del Banco continued to issue basanite. The eruption ended with Duraznero erupting basanite with abundant crustal and mantle xenoliths. The tephrites and basanites from Duraznero and Llano del Banco show narrow compositional ranges and def'me a bhmodal suite. Each batch ascended and evolved separately without significant intermixing, as did the Hoyo Negro basanite, which formed at lower degrees of melting. The magmas fractionated clinopyroxene + olivine + kaersutite + Ti-magnetite at 600-800 MPa and possibly 800-1100 MPa. Abundant reversely zoned phenocrysts reflect mixing with evolved melts at mantle depths. Probably as early as 1936, Hoyo Negro basanite entered the deep rift system at 200-3 50 MPa. Some shallower pockets of this basanite evolved to phonotephrite through differentiation and assimilation of wall rock. A few months prior to eruption, a mixing event in the mantle may have triggered the final ascent of the magmas. Most of the erupted tephrite and basanite ascended from mantle depths within hours to days without prolonged storage in crustal reservoirs. The Cumbre Vieja rift zone differs from the rift zones of Kilauea volcano (Hawaii) in lacking a summit caldera or a summit reservoir feeding the rift system and in being smaller and less active with most of the rift magma solidifying between eruptions. and typically, though not always, results in an eruption. Much magma is stored in the deeper part of the rift system, forming crystal mush or isolated pockets which differentiate and then either solidify or are erupted [Wright and Fiske, 1971; Ryan, 1988; Delaney et al., 1990]. Mixing of distinct magmas in the summit reservoir and in the deep rift is important in controlling the composition of the erupted lavas, although some magmas bypass the summit reservoir [Garcia et al., 1989, 1996]. La Palma has a well-developed active volcanic rift zone along a north-south trending ridge [Middlemost, 1972; Carracedo, 1994]. Only a few studies, however, have addressed magma transport and storage beneath and within this rift system [Klagel et al., 1997] and the evolution of its magmas [Praegel, 1986; Elliott, 1991]. Here we discuss the petrology, geochemistry, and magma supply dynamics of the 1949 eruption, which serves as a case study for complex rift zone eruptions on La Palma. We show how the erupted magmas can be related to storage, fractionation, and mixing in reservoirs within the mantle and the crust and compare the situation on La Palma to that of Kilauea. The 1949 eruption is of particular interest because a variety of eruptive processes occurred during the 37 days of activity and because eyewitness accounts indicate an interconnection of widely sepa-5997 5998 KLOGEL ET AL.' THE 1949 RIFT ZONE ERUPTION ON LA PALMA N o 5 km I Historic eruption ß [--• Recent sediments I----] Cumbre Vieja series '""• Older volcanic series • Basal complex -,--,-Cliff / steep ridge ---Cumbre Vieja rift zone 1949 Santa Cruz 1585 1712 / M25 Lanzarote•/S 1 29 La Palma/... •[ ._ / c;anary Islands •/'/ •Tenerife v•t / • Fu rt 28 L GO•m•er• '• e e enura/ • to 0.7 Ma) which includes the Taburiente shield volcano, the Bejenado edifice, and the Cumbre Nueva series; and (3) the Cumbre Vieja series (0.7 Ma to present) which is confined to the southern half of the island [Hausen, 1969; Middlemost, 1972; islands located off the northwestern African continental shelf Abdel-Monem et al., 1972; $chmincke, 1976; Staudigel and (Figure 1). All islands are underlain by oceanic crust as indicated by tholeiitic mid-ocean ridge basalt (MORB) gabbro xenoliths occurring on Lanzarote, Gran Canaria, and La Palma [Hoernle, 1998; Schmincke et al., 1998]. The age of the crust is bracketed by paleomagnetic anomalies S 1 (175 Ma), between the easternmost islands and the African coast, and M25 (155 Ma) between La Palma and Hierro, which are the westernmost and youngest islands [Roeset, 1982; Klitgord and Schouten, 1986]. The geology of the Canary Islands is summarized by Schmincke [ 1976, 1982]. Schmincke, 1984; Ancochea et al., 1994; Carracedo et al., 1999] (Figure 1). The north-south trending Cumbre Vieja ridge consists dominantly of mafic lava flows, cinder cones, and several phonolitic plugs. Lava compositions range from basanite to phonolite with clinopyroxene + olivine + kaersutitic amphibole as the major phenocryst phases. Most historic eruptions were chemically and mineralogically zoned, commonly carrying mantle and crustal xenoliths during the final eruptive phase [Hernanddz-Pacheco and Valls, 1982; Ibarrola, 1974; Praegel, 1986]. The Cumbre Vieja is interpreted as a volcanic rift zone because vents