Northeast Crater Research Articles

Combined discrete and continuous gravity observations at Mount Etna

Systematic investigation of discrete gravity measurements has continued at Mount Etna since 1986. The network now covers an area of 400 km 2 with about 70 stations 0.5–3 km apart. Mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface (magma level changes within the shallower parts of the feeding conduits) have been identified from these data. Conventional (discrete) microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems. In order to obtain information on the rate at which the volcanic processes (and thus mass transfers) occur, three stations for continuously recording gravity where installed on Mount Etna in 1998. A 16-month long sequence from one of the continuously running stations (PDN, located 2 km from the active northeast crater at the summit of Etna volcano) is presented. After removing the effects of Earth Tide and tilt, the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed. Once the meteorological effects have also been removed, continuous gravity changes are within 10 μGal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station. This example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes.

Thermal infrared mapping of White Island volcano, New Zealand

The first aerial thermal infrared (TIR) survey of White Island volcano was successfully performed during the early morning of 15 April 1992. High spatial resolution (1–2 m) TIR imagery, representative of surface temperatures, and simultaneous visible video imagery were obtained over approximately 75% of the exposed portion of this active volcano. Surface temperatures, ranging from ambient (11.8 °C) to active (95.7 °C), were measured at 12 sites for image calibration purposes.The TIR imagery clearly depicts structurally complex thermal areas within Main Crater. Regions of thermal activity along the northern crater rim and on the northwest, north and northeast crater flanks were also detected. One thermal seepage was observed on the north coast, west of North East Point.A close correlation is demonstrated between the TIR thermal anomalies and present vent locations, prehistoric subcrater boundaries, and the geohydrology of the hydrothermal system hosted in Main Crater. Most of the active 1978/90 Crater Complex was mapped as a high-temperature anomaly, except for one relatively cool area which developed soon after by subsidence and collapse into a major new vent, Princess Crater. Impermeable crater lake sediments are believed to cap the hydrothermal system in parts of the central and eastern subcraters where the TIR map shows appreciable areas at ambient temperatures. An area of high heat flow is located in the south side of the eastern subcrater where steam and gas escape through fractured lavas. The distribution of thermal anomalies in the eastern subcrater suggests that there may have been two smaller craters located within the larger, now filled in, structure.

Volcanic tremors and shocks associated with eruptions at Etna (Sicily), September 1980

Abstract Three strong ash eruptions, superimposed on an otherwise rather quiet state of volcanic activity, took place from the northeast crater of Etna during September 1980. The eruptions lasted only a few hours and were associated with an increase in the amplitudes of volcanic tremors by a factor of 10 compared with the mean value of the preceding months. Special emphasis in the tremor analysis was given to the eruption of September 26, 1980. The time function of the amplitude envelope of the tremors follows a mathematical function which resembles the behaviour of a mechanical oscillator with a resonant period of about 300 s. A detailed spectral analysis of the tremors before, during and after the eruption reveals factors which seem to be associated with the ascent and descent of the tremor sources in the magma columns. The turbulent eruptive magma flow apparently is concentrated in a few dykes and pipes. Their eigenvibrations during an eruption are observed as spectral peaks of small bandwidth, superimposed on the smoother spectrum without a volcanic eruption. An analysis of seismicity shows a maximum in August with epicenters clustering along a NW-SE direction.

SEAN report

The following geophysical and astronomical events were reported byte Scientific Event Alert Network (SEAN), Smithsonian Institution, NHB Stop 129, Washington, D.C. 20560.Volcanic EventsAfter several months of quiescence, Mt. Etna (Italy) began to erupt during the early morning of July 16 from a new vent at 3200‐m elevation, just north of the northeast crater. The new vent, containing a small lava lake, waste source of two lava flows, the larger of which moved east into the Valle del Leone and the smaller to the north. By July 18 the flows had reached about 2 km and 800 m in length, respectively. Shortly after the first lava effusion, Strombolian activity began from the new vent, rapidly increasing in frequency and power. Ejecta reached 600 m in height and covered an area about 1 km in diameter. The explosions had ended by July 20, and lava extrusion ceased July 23–24.

Cinder cone growth modeled after Northeast Crater, Mount Etna, Sicily

The structure, physical properties of ejecta, ballistics, and growth of Northeast crater, a young pyroclastic cone that originated in 1911 near the summit of Mount Etna, Sicily, were studied in order to form a model of volcano cinder cone growth. Four stages of growth were discerned: (1) a simple cone; (2) a cone with an outward-dipping talus slope; (3) destruction of rounded rim by the inward migration of the upper edge of the talus pile; and (4) extension of limits of talus pile beyond the ballistic limit of ejecta trajectories. The model is used to predict the features of lunar and Martian cones, assuming that they erupted under conditions qualitatively similar to Etna's Northeast crater.