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Abstract: In the last part of the 20th century and the beginning of the 21st century, Mt. Merapi in Central-Java Indonesia erupted about every 2–5years. Most of the eruptions were low in explosivity, with VEI-3 or less. Eruptions usually involve the formation of a lava dome, either in the beginning or in the end of the eruptive episode. For the 2006 eruption, the precursory signal was first observed in the middle of the year 2005 with a decrease in EDM slope distances to points on the rim, an increase of seismicity and a possible increase of SO2 emissions. Those early events marked the beginning of a more continuous period of inflation, which led to the eruption. In total, the pre-eruption displacement of the southern rim reached at least 2.4m toward the measuring station in Kaliurang (KAL). From late April until June 2006, a lava dome grew on the summit with a volume that gradually increased until it reached about 4.1millionm3 in 38days. The total of erupted magma was about 5.3millionm3 dense-rock-equivalent (DRE). The dome subsequently collapsed in three steps from June 4 to June 14, leaving an open scar on its southeast side. In this paper we detail the changes of dome morphology that were monitored by taking successive photographs from similar positions. The eruption in 2006 marked a significant change in summit morphology, from west-southwestward opening during the 20th century to the currently southeast orientation. Also, an Mw 6.4 earthquake occurred on 26 May, midway through the eruption, which adds interesting questions about the relationship of the eruption and the earthquake. EDM data from 2006 and previous eruptions show that the summit remains inflated after each eruption, i.e., no significant deflation occurs following eruptions. The lack of post-eruption deflation suggests that magma remains in the shallow parts of the edifice after the eruption. As a result, the complex of summit lava domes and their intrusive roots grow with time and Merapi's rim and summit become progressively more unstable and prone to collapse. [Copyright &y& Elsevier]

The western slope of Cerro Domuyo in northern Patagonia is characterized by thermal springs with boiling waters, Quaternary silicic domes, and pyroclastic deposits that suggest the existence of a geothermal reservoir. According to geochemical studies, the reservoir may have a temperature of 220 °C and one of the largest advective heat fluxes reported for a continental volcanic center. In this paper, we propose a more refined conceptual model for the Domuyo geothermal area, based on a geological survey supported by U Pb, U Th, and Ar Ar geochronology and by magnetotelluric and gravity surveys. Our study indicates that the Domuyo Volcanic Complex (DVC) is a Middle Pleistocene dome complex overlying middle Miocene to Pliocene volcanic sequences, which in turn cover: 1) the Jurassic-Early Cretaceous Neuquén marine sedimentary succession, 2) silicic ignimbrites dated at ~186.7 Ma, and 3) the Paleozoic metamorphic basement intruded by ~288 Ma granite bodies. The volcanic cycle in the DVC is distinctly bimodal, characterized by the emplacement of massive silicic domes and less voluminous olivine basalts on its southern slope. A major collapse of the central dome at ~600 ka produced a voluminous (19.4 km3 and 133 km2) block-and-ash flow, and associated pyroclastic flows, that filled a valley to the southwest at distances up to ~30 km from Cerro Domuyo summit. This was followed by a period of intense effusive activity that formed the Cerro Guitarra, Cerro Las Pampas, Cerro Domo, and Cerro Covunco silicic domes. The last two domes are the youngest and largest edifices, dated at 0.50 Ma (Ar Ar age) and 0.25 Ma (U Th age). Pre-Cenozoic successions were affected by N-S reverse and thrust faults that were later displaced by an ENE-WSW-trending transtensional belt. The basement rocks at the northern termination of the Cordillera del Viento anticlinorium were also displaced towards the east-northeast by this belt, which is observed NNW of Cerro Domuyo. The DVC was emplaced within this zone of crustal weakness. The integration of geologic observations with magnetotelluric and gravity data, allowed us to develop an updated conceptual model of the geothermal system. The geothermal reservoir is inferred at a depth of less than 2 km within pre-Pliocene fractured rocks, bounded by ~WSW-ENE trending faults and sealed by the pyroclastic deposits and rhyolitic lavas of the DVC. The location of most thermal springs is not directly controlled by faults. Instead, flows emerge at the contact between the fractured and faulted basement and the caprock. • The Domuyo Volcanic Complex (DVC) is a silicic dome complex formed in the Pleistocene. • The central dome collapsed at ~600 ka producing a voluminous (19.4 km3) pyroclastic deposit. • The youngest domes were emplaced at ~500 ka and 250 ka. • The DVC was emplaced within a ENE-WSW trending transtensional zone of crustal weakness. • The geothermal reservoir is hosted in pre-Pliocene rocks sealed by the DVC pyroclastics and lavas. [ABSTRACT FROM AUTHOR]

A second extrusive phase of the currently ongoing 1995–2003 eruption of Soufrie`re Hills Volcano (SHV), Montserrat, commenced in mid-November 1999 following ∼19 months during which no fresh lava had reached the surface. By mid-March 2000, a new andesite lava dome constructed within a collapse scar girdled by remnants of the 1995–1998 dome complex had attained an estimated volume of ∼29±3 million m3 (Mm3). On 20 March 2000, during a period of heavy rainfall on the island, a significant collapse event ensued that removed ∼95% of the new lava dome (∼28±3 Mm3) during ∼5 hours of activity that generated ∼40 pyroclastic flows and at least one magmatic explosion. The associated ash cloud reached an altitude of ∼9 km and deposited ash on the island of Guadeloupe to the southeast, and a number of lahars and debris flows occurred in valleys on the flanks of SHV. A large quantity of observational data, including contemporaneous field observations and continuous data from the broadband seismic network on Montserrat, allow a detailed reconstruction of this dome collapse event. In contrast to most of the large dome collapses at SHV, the 20 March 2000 event is distinguished by a lack of short-term precursory elevated seismicity at shallow depths beneath the lava dome. Broadband seismic amplitude data recorded during the event are used to infer the cumulative volume of collapsed dome as the collapse progressed. These data indicate that the high-velocity pyroclastic flows observed at the climax of the event removed by far the largest portion (∼68%) of the lava dome at peak discharge rates (estimated from the seismic record) of ∼2×104 m3 s−1. Following the 20 March 2000 collapse, lava dome growth recommenced immediately and continued without significant interruption until another, larger dome collapse occurred on 29 July 2001. The 29 July 2001 event also coincided with heavy rainfall on Montserrat [Matthews et al. (2002) Geophys. Res. Lett. 29; DOI:10.1029/2002GL014863] and lacked precursory elevated seismic activity. We attribute the initiation of the 20 March 2000 collapse to a prolonged spell of heavy rainfall on the lava dome prior to and during the event. The precise causal mechanism remains controversial, though some combination of mechanical erosion and/or destabilization of a critically poised face of the lava dome, the action of pressurized steam or water on potential failure surfaces within the dome, rapid cooling of hot lava and small phreatic explosions seems likely. Anecdotal evidence exists for other rainfall-induced activity on Montserrat, and the triggering of explosive or pyroclastic flow activity by rainfall has been noted at dome-forming volcanoes elsewhere, including Merapi, Indonesia [Voight et al. (2000) J. Volcanol. Geotherm. Res. 100, 69–138], Unzen, Japan [Yamasato et al. (1997) Papers Meteorol. Geophys. 48], Santiaguito, Guatemala [Smithsonian Institution Global Volcanism Network Bull. 15 (1990)] and Mount St. Helens, USA [Mastin (1994) Geol. Soc. Am. Bull. 106, 175–185]. Hazard mitigation plans at dome-forming volcanoes would therefore benefit from the inclusion of meteorological forecasting and rain monitoring equipment, particularly in the tropics. [Copyright &y& Elsevier]

Cerro Pinto is a Pleistocene rhyolite tuff ring-dome complex located in the eastern Trans-Mexican Volcanic Belt. The complex is composed of four tuff rings and four domes that were emplaced in three eruptive stages marked by changes in vent location and eruptive character. During Stage I, vent clearing produced a 1.5-km-diameter tuff ring that was then followed by emplacement of two domes of approximately 0.2 km each. With no apparent hiatus in activity, Stage II began with the explosive formation of a tuff ring ~2 km in diameter adjacent to and north of the earlier ring. Subsequent Stage II eruptions produced two smaller tuff rings within the northern tuff ring as well as a small dome that was mostly destroyed by explosions during its growth. Stage III involved the emplacement of a 0.04 km dome within the southern tuff ring. Cerro Pinto's eruptive history includes sequences that follow simple rhyolite-dome models, in which a pyroclastic phase is followed immediately by effusive dome emplacement. Some aspects of the eruption, however, such as the explosive reactivation of the system and explosive dome destruction, are more complex. These events are commonly associated with polygenetic structures, such as stratovolcanoes or calderas, in which multiple pulses of magma initiate reactivation. A comparison of major and trace element geochemistry with nearby Pleistocene silicic centers does not show indication of any co-genetic relationship, suggesting that Cerro Pinto was produced by a small, isolated magma chamber. The compositional variation of the erupted material at Cerro Pinto is minimal, suggesting that there were not multiple pulses of magma responsible for the complex behavior of the volcano and that the volcanic system was formed in a short time period. The variety of eruptive style observed at Cerro Pinto reflects the influence of quickly exhaustible water sources on a short-lived eruption. The rising magma encountered small amounts of groundwater that initiated eruption phases. Once a critical magma:water ratio was exceeded, the eruptions became dry and sub-plinian to plinian. The primary characteristic of Cerro Pinto is the predominance of fall deposits, suggesting that the level at which rising magma encountered water was deep enough to allow substantial fragmentation after the water source was exhausted. Isolated rhyolite domes are rare and are not currently viewed as prominent volcanic hazards, but the evolution of Cerro Pinto demonstrates that individual domes may have complex cycles, and such complexity must be taken into account when making hazard risk assessments. [ABSTRACT FROM AUTHOR]

Arthropathy of the ankle joint is commonly observed in people with severe haemophilia. A review of the radiological appearance of ankle arthropathy provides evidence that the changes in the talar bone of the ankle joint are probably due to avascular necrosis. This may arise due to impairment to the arterial supply, as it enters the talar neck, secondary to the increased pressure at the time of haemarthroses. [ABSTRACT FROM AUTHOR]