Sonia Calvari

Chronology and complex volcanic processes during the 2002--2003 flank eruption at Stromboli volcano (Italy) reconstructed from direct observations and surveys with a handheld thermal camera

[1] Effusive activity at Stromboli is uncommon, and the 2002–2003 flank eruption gave us the opportunity to observe and analyze a number of complex volcanic processes. In particular, the use of a handheld thermal camera during the eruption allowed us to monitor the volcano even in difficult weather and operating conditions. Regular helicopter-borne surveys with the thermal camera throughout the eruption have significantly improved (1) mapping of active lava flows; (2) detection of new cracks, landslide scars, and obstructions forming within and on the flanks of active craters; (3) observation of active lava flow field features, such as location of new vents, tube systems, tumuli, and hornitos; (4) identification of active vent migration along the Sciara del Fuoco; (5) monitoring of crater’s inner morphology and maximum temperature, revealing magma level changes within the feeding conduit; and (6) detection of lava flow field endogenous growth. Additionally, a new system developed by A. J. L. Harris and others has been applied to our thermal data, allowing daily calculation of effusion rate. These observations give us new insights on the mechanisms controlling the volcanic system.

Formation of lava tubes and extensive flow field during the 1991–1993 eruption of Mount Etna

Detailed mapping during the 1991–1993 eruption of Mount Etna has shown that there is a relationship between tumuli, ephemeral vents, lava tubes, and their parent lava flows. During this eruption, many tubes formed in stationary, inflated ‘a’a lava flows. Ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows, many of which subsequently developed new tubes. The resulting complex network of tubes, ephemeral vents, and secondary flows was responsible for most of the widening, thickening, and lengthening of the 1991–1993 Etna lava flow field. The supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel-fed lava flow. Our observations suggest that lava tubes play a more important role in the formation of extensive ‘a’a flow fields on Etna than has previously been recognized.

Effusion rate estimations during the 1999 summit eruption on Mount Etna, and growth of two distinct lava flow fields

Detailed studies of the evolution of two major flow fields during the 1999 eruption on Mount Etna provide useful insights into the development of different types of flow fields. During this eruption, two large lava flow fields were emplaced. The Eastern flow field, which formed between February and November, was erupted from three primary vents at the base of the Southeast Cone, one of four eruptive centres in the summit region of Mount Etna. This compound flow field was characterised by a complex tube network, skylights, ephemeral vents and tumuli. Between mid-October and early November, while the Eastern flow field was still active, another flow field was erupted from the western rim of the Bocca Nuova, one of the other eruptive centres. This Western flow field was emplaced during one month of discontinuous activity and is composed of discrete, channel-fed a′a flow units that formed a fan-shaped flow field. Major periods of flow advance within this flow field took place during phases of relatively high flow rate that lasted a few hours to days. The discontinuous supply prevented the formation of lava tubes within this flow field. The Eastern and Western lava flow fields from the Southeast Cone and Bocca Nuova have distinctive morphologies that reflect their emplacement mechanisms. Many of these morphological features are large enough to be seen on aerial photographs. This has implications for assessing the emplacement conditions of older flow fields on Earth and on other planets.

Lava tube morphology on Etna and evidence for lava flow emplacement mechanisms.

Lava tubes play a pivotal role in the formation of many lava flow fields. A detailed examination of several compound ‘a‘a lava flow fields on Etna confirmed that a complex network of tubes forms at successively higher levels within the flow field, and that tubes generally advance by processes that include flow inflation and tube coalescence. Flow inflation is commonly followed by the formation of major, first-order ephemeral vents which, in turn, form an arterial tube network. Tube coalescence occurs when lava breaks through the roof or wall of an older lava tube; this can result in the unexpected appearance of vents several kilometers downstream. A close examination of underground features allowed us to distinguish between ephemeral vent formation and tube coalescence, both of which are responsible for abrupt changes in level or flow direction of lava within tubes on Etna. Ephemeral vent formation on the surface is frequently recorded underground by a marked increase in size of the tube immediately upstream of these vents. When the lining of an inflated tube has collapsed, ‘a‘a clinker is commonly seen in the roof and walls of the tube, and this is used to infer that inflation has taken place in the distal part of an ‘a‘a lava flow. Tube coalescence is recognised either from the compound shape of tube sections, or from breached levees, lava falls, inclined grooves or other structures on the walls and roof. Our observations confirm the importance of lava tubes in the evolution of extensive pahoehoe and ‘a‘a flow fields on Etna.

Birth, growth and morphologic evolution of the ‘Laghetto’ cinder cone during the 2001 Etna eruption

We have undertaken detailed observations of the formation of the ‘Laghetto’ cinder cone, a new cone that formed during a 2-week period of intense activity in Piano del Lago, on the upper slopes of Mount Etna in summer 2001. We describe the events leading to the formation of a small graben, the formation of pit craters on the base of the graben, the onset of phreatomagmatic activity, a transition to intense Strombolian activity, and a return to phreatomagmatic activity as the eruption came to an end. We discuss the reasons for these transitions, and describe the morphological development of the cone during these events. Arcuate cracks on the southern part of the cone were related to withdrawal of magma at the end of the eruption. Other slope instabilities that developed during the eruption include the formation of small radial grain flows on the outer flanks of the cone and the collapse into the crater of part of the crater rim. Some of the failure planes we observed were first identified using a FLIR TM 695 thermal infrared camera. This is the first time that infrared thermography has been used to detect instability of volcanic structures. Results obtained during this test case demonstrate that thermal cameras are a very useful tool for studies of volcanic instability.

The 2007 Stromboli eruption: Event chronology and effusion rates using thermal infrared data

Accepted for publication in Journal of Geophysical Research. Copyright (2009) American Geophysical Union. Further reproduction or electronic distribution is not permitted.

Heat loss measured at a lava channel and its implications for down-channel cooling and rheology

During May 2001 we acquired 2016 thermal images over an ~8-h-long period for a section of active lava channel on Mount Etna (Italy). We used these to extract surface temperature and heat-loss profi les and thereby calculate core cooling rates. Flow surface temperatures declined from ~1070 K at the vent to ~930 K at 70 m. Heat losses were dominated by radiation (5 × 10 W m) and convection (~10 W/m). These compare with a heat gain from crystallization of 6 × 10 W/m. The imbalance between sinks and sources gives core cooling (δT/δx) of ~110 K/km. However, cooling rate per unit distance also depends on fl ow conditions, where we distinguished: (1) unimpeded, high-velocity (~0.2 m/s) fl ow with low δT/δx (0.3 K/m); (2) unimpeded, low-velocity (~0.1 m/s) fl ow with higher δT/δx (0.5 K/m); (3) waning, insulated fl ow at low velocity (~0.1 m/s) with low δT/δx (0.3 K/m); and (4) impeded fl ow at low velocity (<0.1 m/s) with higher δT/δx (0.4 K/m). Our data allow us to defi ne three thermal states of fl ow emplacement: insulated, rapid, and protected. Insulated is promoted by the formation of hanging blockages and coherent roofs. During rapid emplacement, higher velocities suppress cooling rates, and δT/δx can be tied to mean velocity (V mean ) by δT/δx = aV mean . In the protected case, deeper, narrow channels present a thermally effi cient channel, where δT/δx can be assessed using the ratio of channel width (w) to depth (d) in w/d = aδT/δx.

The application of a long-range laser scanner for monitoring volcanic activity on Mount Etna

Abstract There is a requirement for rapid remote monitoring of ground deformation of volcanoes, especially during eruptions. A long-range reflector-less laser scanning instrument, manufactured by Riegl Laser Measurement Systems, was used on Mount Etna in October 2000, and its potential for monitoring ground surface changes associated with volcanic activity was evaluated. The 3DLM LR1 scanner system can measure distances up to 2 km with an accuracy of ±25 mm in typical conditions. Measurement rates range from 1 point per second at 2 km to 4 points per second at 10 m. The system also records reflective intensity, and this proved useful in distinguishing between different types of volcanic material. Cloud and gas obscured some measurements, but the scanning nature of the instrument, coupled with effective data filtering software, allowed robust digital terrain models to be created.

Development of tumuli in the medial portion of the 1983 aa flow-field, Mount Etna, Sicily

A number of tumuli formed on the aa-dominated lava fan complex which developed in the medial zone of the 1983 flow-field of Mount Etna during the later stages of the eruption. This complex flow-field formed on shallow sloping ground below a scarp between 1900 and 1700 m asl. A major tube system fed a branching tube network in the fan complex. Numerous tumuli and break-outs of lava formed in the fan. Three main types of tumulus are identified: (1) Focal tumuli, which are formed from the break-up and uplift of ‘old’, thick lava crust and themselves become sustained sites for the distribution of lava both as flows and within distributary tubes. These focal tumuli are significant centres associated with major tubes. (2) Satellite tumuli, which are typically elongate, whale-back shaped features that branch out from focal tumuli. These satellite tumuli were initially lava flows erupted from a focal tumulus. The crust of the flow slowed or came to a halt and the rigid crust became uplifted and fractured, forming a dome-shaped ridge feature. These satellite tumuli continued to be fed from the focal tumulus and became sites of lava emission with numerous break-outs. (3) Distributary tumuli formed on the fan associated with short-lived break-outs from tubes and are relatively simple structures formed from limited effusion of toey lobes and pahoehoe lava. The major tumuli on the fan complex show distinct dilation fractures. The fracture surfaces provide good exposure of the crust and three distinct zones are recognised – an upper zone showing columnar jointing, a middle zone consisting of planar fracture surfaces and a basal zone with distinctive banded planar fracture surfaces showing evidence of both brittle and ductile formation. Using these data a model is proposed for tumulus growth. Field analysis of the fan complex shows how it was fed by a branching tube system, leading to flow thickening, formation of tumuli and numerous ephemeral boccas.

Debris-avalanche deposits of the Milo Lahar sequence and the opening of the Valle del Bove on Etna volcano (Italy)

Previously undescribed debris-avalanche deposits occur in two locations downslope from the open end of the Valle del Bove. These outcrops comprise unstratified, ungraded deposits of metre-scale lava blocks in a matrix of weathered and fractured lava clasts. The avalanche deposits are unconformably overlain by matrix- to clast-supported conglomerates, representing debris-flow and interbedded fluvial deposits, that constitute most of the Milo Lahar sequence. We present evidence that the Milo Lahar sequence, which crops out just at the exit of the Valle del Bove, formed during the opening and enlargement of this depression. The presence of the avalanche deposits at the base of the Milo Lahar sequence indicates that catastrophic landslides were involved in the formation of the Valle del Bove. The composition of lavas in the debris avalanche deposits is similar to that of most of the Ellittico volcanic sequence exposed along the northern wall of the Valle del Bove. Radiocarbon dates of 8400 and 5300 years BP from the base and top, respectively, of the debris-flow sequence indicate that the Milo Lahars are correlative with the exposed part of the Chiancone deposit. The basal lahars of the Chiancone, which contain lava blocks whose compositions partially overlap that of blocks in the avalanche deposits, may have formed by water concentration in the distal end of the avalanche causing transformation to debris, or alternatively by reworking of the avalanche deposit.