Vesicular komatiites, 3.5-Ga Komati Formation, Barberton Greenstone Belt, South Africa: inflation of submarine lavas and origin of spinifex zones

Komatiites of the 3.5-Ga Komati Formation are ultramafic lavas (>23% MgO) erupted in a submarine, lava plain environment. Newly discovered vesicular komatiites have vesicular upper crusts disrupted by synvolcanic structures that are similar to inflation-related structures of modern lava flows. Detailed outcrop maps reveal flows with upper vesicular zones, 2-15 m thick, which were (1) rotated by differential inflation, (2) intruded by dikes from the interior of the flow, (3) extended, forming a flooded graben, and/or (4) entirely engulfed. The largest inflated structure is a tumulus with 20 m of surface relief, which was covered by a compound flow unit of spinifex flow lobes. The lava that inflated and rotated the upper vesicular crust did not vesiculate, but crystallized as a thick spinifex zone with fist-size skeletal olivine. Instead of representing rapidly cooled lava, the spinifex zone cooled slowly beneath an insulating upper crust during inflation. Overpressure of the inflating lava may have inhibited vesiculation. This work describes the oldest vesicular komatiites known, illustrates the first field evidence for inflated structures in komatiite flows, proposes a new factor in the development of spinifex zones, and concludes that the inflation model is useful for understanding the evolution of komatiite submarine flow fields.     

东太平洋Juan de Fuca板块的磁变研究

作为EMSLAB电磁感应国际合作计划的一部分,通过对海底观测的三分量变化地磁场的分析,构制了横跨Juan de Fuca洋脊、Juan de Fuca板块到板块俯冲带的三条地磁转换函数剖面,计算了各个测点的地磁场感应矢量。结果表明,Juan de Fuca板块的东、西两部分的浅部电性结构是有差异的,近海岸线的东区更导电;而深部电性结构是相对均匀的。这一结果与由大地电磁资料计算得到的二维模型剖面是一致的。     

Development of the 1990 Kalapana Flow Field,Kilauea Volcano,Hawaii

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m³/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.     

Nontronite from a low-temperature hydrothermal system on the Juan de Fuca Ridge

A deposit of Fe-rich, Al-poor, hydrothermal nontronite was recovered from the Juan de Fuca Ridge. Analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities. The deposit is located near the tip of a propagating segment of the Juan de Fuca Ridge. Rare earth elements and Sr isotopes indicate that the nontronite precipitated from seawater. A formation temperature of 57°C is suggested by oxygen isotopic composition. The low-temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment. More mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low-temperature systems.     

Submarine lineated sheet flows: a unique lava morphology formed on subsiding lava ponds

 Lineated sheet flows are flat-lying, glassy lava flows characterized by a regular surface pattern of parallel grooves or furrows aligned with the flow direction. They are unique to the submarine environment. We propose that the lineations are developed within the collapsed interiors of partially ponded lobate sheet flows that initially inflate and then drain out during emplacement. During lava drainout, the original lobate crust founders and a new crust begins to grow on the subsiding lava surface. Lineated flow texture is created where molten lava emerges laterally from beneath a growing crust. The lineations are formed by raking of the emerging lava surface by irregularities on the bottom edge of the crust and are preserved owing to rapid chilling by seawater. Therefore, lineated sheet flows are the product of a specific sequence of events over a short period of time during the course of a deep submarine eruption. Received: 23 November 1998 / Accepted: 22 February 1999     

Evolution of Mount Fuji,Japan: Inference from drilling into the subaerial oldest volcano,pre‐Komitake

A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km³/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO₂, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO₂. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.     

The initial cooling of pahoehoe flow lobes

 In this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows. The accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation. This model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data. We find that the only significant processes are (a) heat loss by thermal radiation, (b) heat loss by atmospheric convection, (c) heat transport within the flow by conduction with temperature and porosity-dependent thermal properties, and (d) the release of latent heat during crystallization. The numerical model is better able to reproduce field measurements made in Hawai'i between 1989 and 1993 than other published thermal models. By adjusting one parameter at a time, the effect of each of the input parameters on the cooling rate was determined. We show that: (a) the surfaces of porous flows cool more quickly than the surfaces of dense flows, (b) the surface cooling is very sensitive to the efficiency of atmospheric convective cooling, and (c) changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures. These model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes (Jones 1992, 1993). The predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification, and the model provides a tool to begin studies of the dynamic crystallization of real lavas. Future versions of the model can also be made applicable to extraterrestrial, submarine, silicic, and pyroclastic flows. Received: 26 November 1994 / Accepted: 1 December 1995     

Scoria cone formation through a violent Strombolian eruption: Irao Volcano, SW Japan

Scoria cones are common volcanic features and are thought to most commonly develop through the deposition of ballistics produced by gentle Strombolian eruptions and the outward sliding of talus. However, some historic scoria cones have been observed to form with phases of more energetic violent Strombolian eruptions (e.g., the 1943–1952 eruption of Parícutin, central Mexico; the 1975 eruption of Tolbachik, Kamchatka), maintaining volcanic plumes several kilometers in height, sometimes simultaneous with active effusive lava flows. Geologic evidence shows that violent Strombolian eruptions during cone formation may be more common than is generally perceived, and therefore it is important to obtain additional insights about such eruptions to better assess volcanic hazards. We studied Irao Volcano, the largest basaltic monogenetic volcano in the Abu Monogenetic Volcano Group, SW Japan. The geologic features of this volcano are consistent with a violent Strombolian eruption, including voluminous ash and fine lapilli beds (on order of 10^?1 km³ DRE) with simultaneous scoria cone formation and lava effusion from the base of the cone. The characteristics of the volcanic products suggest that the rate of magma ascent decreased gradually throughout the eruption and that less explosive Strombolian eruptions increased in frequency during the later stages of activity. During the eruption sequence, the chemical composition of the magma became more differentiated. A new K–Ar age determination for phlogopite crystallized within basalt dates the formation of Irao Volcano at 0.4?±?0.05 Ma.     

Lava tubes,terraces and megatumuli on the 1614–24 pahoehoe lava flow field,Mount Etna,sicily

The 1614–1624 lava flow of Mt. Etna was formed during a long-duration flank eruption involving predominantly pahoehoe flows which produced unusual surface features including mega-tumuli (here defined) and terraces. Detailed mapping of the flow units, surface features, and associated tubes reveals a complex sequence of emplacement for the field. The stair-stepped terraces appear to have been formed as a consequence of self-damming of tube-fed flows which developed «perched» ponds of lava. Surges of lava through tubes elevated sections of crusted lava at the distal ends of the flow to generate tumuli, some as high as 130 m, as a consequence of pressure via «hydrostatic head» conditions within the tube. Although pahoehoe lavas and the related features described here are atypical of Mt. Etna, they may reflect styles of eruption and lava emplacement found on volcanoes elsewhere.     

Rates of volcanic activity along the southwest rift zone of Mauna Loa volcano,Hawaii

Flow by flow mapping of the 65-km-long anbaerial part of the southwest rift zone and adjacent flanks of Mauna Loa Volcano, Hawaii, and about 50 new¹⁴C dates on charcoal from beneath these flows permit estimates of rates of lava accumulation and volcanic growth over the past 10,000 years. The sequence of historic eraptions along the southwest rift zone, beginning in 1868, shows a general pattern of uprift migration and increasing eruptive volume, culminating in the great 1950 eruption. No event comparable to 1950, in terms of volume or vent length, is evident for at least the previous 1,000 years. Rates of lava accumulation during the historic period were several times higher than the average rate for the preceding few thousand years along the southwest rift zone and adjacent flanks. Rates of lava accumulation along the zone have been subequal to those of Kilauea Volcano during the historic period but they were much lower in late prehistoric time (anpubl. Kilauea data byR.T. Holcomb). Thus, only about 30% of the surface of the southwest side of Mauna Loa has been covered by lava during the last 1,000 years, as contrasted with about 90% of the subaerial surface of Kilauea. Rates of surface covering and volcanic growth have been markedly asymmetric along Mauna Loa’s southwest rift zone. Accumulation rates have been about half again as great on the northwest side of the rift zone in comparison with the southeast side. The difference apparently reflects a westward lateral shift of the rift zone of Mauna Loa away from Kilauea Volcano, which may have acted as a barrier to symmetrical growth of the rift zone.     

Pahoehoe flows from the central Paraná Continental Flood Basalts

Inflated and compound pahoehoe flows have been identified within the central Paraná Continental Flood Basalts based upon their morphology, surface features, and internal zonation. Pahoehoe flow features have been studied at five localities in the western portion of Paraná State, Brazil: Ponte Queimada, Toledo, Rio Quitéria, Matelandia and Cascavel. We have interpreted the newly recognized flow features using concepts of Hawaiian pahoehoe formation and emplacement that have been previously applied to the Columbia River Basalt and Deccan Plateau. Surface features and/or internal structure typical from pahoehoe lavas are observed in all studied areas and features like inflation clefts, squeeze-ups, breakouts, and P-type lobes with two levels of pipe vesicles are indicative of inflation in these flows. The thinner, compound pahoehoe flows are predominantly composed of P-type lobes and probably emerged at the end of large inflated flows on shallow slopes. The presence of vesicular cores in the majority of compound lobes and the common occurrence of segregation structures suggests high water content in the pahoehoe lavas from the central PCFB. More volcanological studies are necessary to determinate the rheology of lavas and refine emplacement models.Editorial responsibility: C. Kilburn     

Propagating rift explanation for the tectonic evolution of the northeast Pacific—the pseudomovie

We have developed a new computer graphic technique to use in reconstructing plate tectonic evolution and to make movies illustrating this evolution. Using this technique, we have deciphered the evolutionary history of the Juan de Fuca area in the northeast Pacific, and show that a combination of seafloor spreading and rift propagation can explain this seemingly complex area as a simple consequence of the interaction of two rigid plates.     

Basanite glaciovolcanism at Llangorse mountain,northern British Columbia,Canada

The Llangorse volcanic field is located in northwest British Columbia, Canada, and comprises erosional remnants of Miocene to Holocene volcanic edifices, lava flows or dykes. The focus of this study is a single overthickened, 100-m-thick-valley-filling lava flow that is Middle-Pleistocene in age and located immediately south of Llangorse Mountain. The lava flow is basanitic in composition and contains mantle-derived peridotite xenoliths. The lava directly overlies a sequence of poorly sorted, crudely bedded volcaniclastic debris-flow sediments. The debris flow deposits contain a diverse suite of clast types, including angular clasts of basanite lava, blocks of peridotite coated by basanite, and rounded boulders of granodiorite. Many of the basanite clasts have been palagonitized. The presence and abundance of clasts of vesicular to scoriaceous, palagonitized basanite and peridotite suggest that the debris flows are syngenetic to the overlying lava flow and sampled the same volcanic vent during the early stages of eruption. They may represent lahars or outburst floods related to melting of a snow pack or ice cap during the eruption. The debris flows were water-saturated when deposited. The rapid subsequent emplacement of a thick basanite flow over the sediments heated pore fluids to at least 80–100°C causing in-situ palagonitization of glassy basanite clasts within the sediments. The over-thickened nature of the Llangorse Mountain lavas suggests ponding of the lava against a down-stream barrier. The distribution of similar-aged glaciovolcanic features in the cordillera suggests the possibility that the barrier was a lower-elevation, valley-wide ice-sheet.     

Deformation structures associated with the Tazo landslide (La Gomera, Canary Islands)

Deformation structures below the basal plane of gravitational slides can provide useful information about the state of stress undergone by rocks prior to the sliding process and about the triggering forces acting at each particular sliding event. In the present work we conducted a structural analysis of the rocks below the surface of the gravitational slide of Tazo (La Gomera, Canary Islands) and determined the epigenetic processes involved in the filling of the amphitheatre. We also inferred the possible triggering phenomena related to the Tazo landslide. The rocks located below the surface of the gravitational slide of Tazo -i.e., the basaltic lava flows, sills and dikes of the Lower Old Edifice and the submarine volcanic rocks, gabbros, pyroxenites and dikes of the Basal Complex of La Gomera- are strongly deformed close to this sliding surface. The lava flows and dikes of the Lower Old Edifice are folded, with fault breccias and gouges, and locally foliated, defining the sliding surface. The dikes of the Basal Complex are also folded, and the gabbros and pyroxenites are affected by a large number of small faults. In the Basal Complex, the sliding surface is defined by a foliated granular gouge. In the damage zone, the Basal Complex rocks show an incipient fracture cleavage. The sliding amphitheatre has been filled by the debris avalanche or cohesive debris flow generated within the slide, as well as by later debris flows, hyperconcentrated flows, sheet flows, and by interspersed lava flows from the Upper Old Edifice. We suggest here that the collapse of the north-western flank of the Lower Old Edifice at Tazo could in part have been triggered by continuous magma injection, associated with the emplacement of dikes in a rift zone with an ENE-WSW direction, enhanced by the mechanical weakness of the Basal Complex unit, which was affected by hydrothermal metamorphism under greenschist facies conditions and by the displacement along the Montaña de Alcalá and Guillama normal faults, which are deeply entrenched in the altered rocks of the Basal Complex.     

Lava tube shatter rings and their correlation with lava flux increases at Kīlauea Volcano,Hawai‘i

Shatter rings are circular to elliptical volcanic features, typically tens of meters in diameter, which form over active lava tubes. They are typified by an upraised rim of blocky rubble and a central depression. Prior to this study, shatter rings had not been observed forming, and, thus, were interpreted in many ways. This paper describes the process of formation for shatter rings observed at Kīlauea Volcano during November 2005–July 2006. During this period, tilt data, time-lapse images, and field observations showed that episodic tilt changes at the nearby Pu‘u ‘Ō‘ō cone, the shallow magmatic source reservoir, were directly related to fluctuations in the level of lava in the active lava tube, with periods of deflation at Pu‘u ‘Ō‘ō correlating with increases in the level of the lava stream surface. Increases in lava level are interpreted as increases in lava flux, and were coincident with lava breakouts from shatter rings constructed over the lava tube. The repetitive behavior of the lava flux changes, inferred from the nearly continuous tilt oscillations, suggests that shatter rings form from the repeated rise and fall of a portion of a lava tube roof. The locations of shatter rings along the active lava tube suggest that they form where there is an abrupt decrease in flow velocity through the tube, e.g., large increase in tube width, abrupt decrease in tube slope, and (or) sudden change in tube direction. To conserve volume, this necessitates an abrupt increase in lava stream depth and causes over-pressurization of the tube. More than a hundred shatter rings have been identified on volcanoes on Hawai‘i and Maui, and dozens have been reported from basaltic lava fields in Iceland, Australia, Italy, Samoa, and the mainland United States. A quick study of other basaltic lava fields worldwide, using freely available satellite imagery, suggests that they might be even more common than previously thought. If so, this confirms that episodic fluctuation in lava effusion rate is a relatively common process at basaltic volcanoes, and that the presence of shatter rings in prehistoric lava flow fields can be used as evidence that such fluctuations have occurred.     

Thermal–mechanical modeling of cooling history and fracture development in inflationary basalt lava flows

Thermal–mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect ratios (width divided by thickness), typically < 5. Four fracture types typically develop: column-bounding, column-normal, entablature (all of which are cooling fractures), and inflation fractures. Cooling fractures provide a proxy for isotherms during cooling and produce patterns that are strongly influenced by flow aspect ratio. Inflation fractures are induced by lava pressure-driven inflationary events and introduce a thermal perturbation to the flow interior that is clearly evidenced by fracture patterns around them. Inflation fracture growth occurs incrementally due to blunting of the lower tip within viscoelastic basalt, allowing the inflation fracture to pivot open. The final stage of growth involves propagation beyond the blunted tip towards the stress concentration at the tapered tip of a lava core, resulting in penetration of the core that causes quenching of the lava and the formation of a densely fractured entablature. We present numerical models that include the effects of inflation fractures on lava cooling and which support field-based inferences that inflation fractures depress the isotherms in the vicinity of the fracture, cause a subdivision of the lava core, control the location of the final portion of the lava flow to solidify, and cause significant changes in the local cooling fracture orientations. In addition to perturbing isotherms, inflation fractures cause a lava flow to completely solidify in a shorter amount of time than an identically shaped flow that does not contain an inflation fracture.     

Lava penetrating water: the different behaviours of pāhoehoe and ‘a‘ā at the Nesjahraun, Tingvellir, Iceland

The Nesjahraun is a basaltic lava flow erupted from a subaerial fissure, extending NE along the Tingvellir graben from the Hengill central volcano that produced pāhoehoe lava followed by ‘a‘ā. The Nesjahraun entered Iceland’s largest lake, Tingvallavatn, along its southern shore during both phases of the eruption and exemplifies lava flowing into water in a lacustrine environment in the absence of powerful wave action. This study combines airborne light detection and ranging, sidescan sonar and Chirp seismic data with field observations to investigate the behaviour of the lava as it entered the water. Pāhoehoe sheet lava was formed during the early stages of the eruption. Along the shoreline, stacks of thin (5–20 cm thick), vesicular, flows rest upon and surround low (<5 m) piles of coarse, unconsolidated, variably oxidised spatter. Clefts within the lava run inland from the lake. These are 2–5 m wide, >2 m deep, ∼50 m long, spaced ∼50 m apart and have sub-horizontal striations on the walls. They likely represent channels or collapsed tubes along which lava was delivered into the water. A circular rootless cone, Eldborg, formed when water infiltrated a lava tube. Offshore from the pāhoehoe lavas, the gradient of the flow surface steepens, suggesting a change in flow regime and the development of a talus ramp. Later, the flow was focused into a channel of ‘a‘ā lava, ∼200–350 m wide. This split into individual flow lobes 20–50 m wide along the shore. ‘A‘ā clinker is exposed on the water’s edge, as well as glassy sand and gravel, which has been locally intruded by small (<1 m), irregularly shaped, lava bodies. The cores of the flow lobes contain coherent, but hackly fractured lava. Mounds consisting predominantly of scoria lapilli and the large paired half-cone of Grámelur were formed in phreatomagmatic explosions. The ‘a‘ā flow can be identified underwater over 1 km offshore, and the sidescan data suggest that the flow lobes remained coherent flowing down a gradient of <10°. The Nesjahraun demonstrates that, even in the absence of ocean waves, phreatomagmatic explosions are ubiquitous and that pāhoehoe flows are much more likely to break up on entering the water than ‘a‘ā flows, which, with a higher flux and shallow underlying surface gradient, can penetrate water and remain coherent over distances of at least 1 km.     

The Negros de Aras Nuée Ardente deposits: a cataclysmic eruption of Socompa volcano (Andes of Atacama,Chile)

Studies of ERT Satellite photographic documents and of acrial photographs with complementary lield work reveal the presence of recent very large nuée ardente deposits north-west of Socompa Volcano (Andean Cordillera of Atacama, northern Chile). Three zones are distinguishable from the bottom of Socompa Volcano to the front of the nuée ardente deposits: 1) pumice blocks are covered with parallel ridges of debris (lava blocks) from the north-western flank of Socompa Volcano, 2) pumice blocks lie upon small cones and flows from El Negrillar volcanoes located inside the graben of Negros de Aras, 3) pumice flow threads its way between cones and flows from El Negrillar volcanoes and stops more than 40 km away from the base of Socompa Volcano. The calculated thermal energy of this cruption is 7.9 × 10²⁵ ergs, being in the range of of the most important recorded eruptions on earth. The pumice is almost aphyric (rare plagioclase, hypersthene and hornblende phenocrysts) and is of dacite composition lying pertectly on the K₂O-SiO₂ trend of the Socompa Volcano. Trace and major element data of the pumice are similar to those of two dacites from a pre-nuée lava flow and a post-nuée lava dome of Socompa Volcano and support a common magmatic origin with the Socompa Volcano lavas. A relative chronology is proposed.     

Emplacement and inflation of natrocarbonatitic lava flows during the March–April 2006 eruption of Oldoinyo Lengai,Tanzania

The most voluminous eruption of natrocarbonatite lava hitherto recorded on Earth occurred at Oldoinyo Lengai in March–April 2006. The lava flows produced in this eruption range from blocky 'a'a type to smooth-surfaced inflated pahoehoe. We measured lava inflation features (i.e. one tumulus and three pressure ridges) that formed in the various pahoehoe flows emplaced in this event. The inflation features within the main crater of Oldoinyo Lengai are relatively small-scale, measuring 1-5 m in width, 2.5–24.4 m in length and with inflation clefts less than 0.4 m deep. Their small sizes are in contrast to a tumulus that formed on the northwestern slope of the volcano (situated ~1140 m below the crater floor). The tumulus is roughly circular, measures 17.5 × 16.0 m, and is cut by a 4.4 m deep axial inflation cleft exposing two separate flow units. We measured the elastic properties (i.e. shear- and bulk moduli) of natrocarbonatitic crust and find that these are similar to those reported for basaltic crust, and that there is no direct correlation between magmastatic head and pressure required to form tumuli. All inflated flows in the 2006 event were confined by lateral barriers (main crater, erosional channel or erosional gully) suggesting that the two most important factors for endogenous growth in natrocarbonatitic lava flows are (1) lateral barriers that prevent widening of the flow, and (2) influx of new material beneath the viscoelastic and brittle crust.     

Documenting surface magmatic activity at Mount Etna using ATSR remote sensing

Analysis of thermally generated night-time volcanic radiances recorded with a 1-km pixel size at 1.6 and 11 µm during 1991-1993 and 1996-1999 for Mount Etna shows that lava flows extending beyond the summit craters can be distinguished from vent activity. The two phenomena plot in different regions of feature space when the mean volcanic radiance (per anomalous pixel) at 11 µm is plotted against the mean volcanic radiance at 1.6 µm. The distinct feature space characteristics of lava flow fields are apparent within 1-2 days of the onset of each effusive event. Such a plot also enables lava flow fields being fed by open channels to be distinguished from tube-fed flow fields. Rank order analysis of the total 1.6-µm volcanic radiance series shows that vent activity and lava flows belong to different populations, and offers further scope for remotely identifying changes in eruptive state.