Distinct activity phases during the recent geologic history of a Gulf of Mexico mud volcano

Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m²) surrounded by a continuous bed of methanotrophic mussels (Bathymodiolus childressi) covering 434 m² and a patchy bed covering an additional 214 m² of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m³, while the middle and upper stages deposited 7700 and 20,400 m³, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ¹⁴C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages.     

五大连池火山群的构造环境与喷发机理

五大连池火山群位于松辽裂谷的北端，这里的火山活动同裂谷的形成与发展密切相关五大连池火山区发育着典型的“Ｘ”型断裂，其次是经向张断裂和纬向压断裂，它们是同一应力场作用下的产物，本文提出了“Ｘ”型断裂的形成与发展过程，并认为五大连池区处于“Ｘ”型断裂发展的第二阶段，即处于剪切应力的最大值阶段，两组断裂呈正交。     

Englacial vs lacustrine origin of volcanic table mountains: evidence from iceland

Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes" in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to 300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake, a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting. The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes. Received: 10 June 1997 / Accepted: 28 July 1998     

The 1999 and 2000 eruptions of Mount Cameroon: eruption behaviour and petrochemistry of lava

Mount Cameroon (4,095 m high and with a volume of ~1,200 km³) is one of the most active volcanoes in Africa, having erupted seven times in the last 100 years. This stratovolcano of basanite and hawaiite lavas has an elliptical shape, with over a hundred cones around its flanks and summit region aligned parallel to its NE--SW-trending long axis. The 1999 (28 March–22 April) eruption was restricted to two sites: ~2,650 m (site 1) and ~1,500 m (site 2). Similarly, in the eruption in 2000 (28 May–19 June), activity occurred at two sites: ~4,095 m (site 1) and ~3,300 m (site 2). During both eruptions, the higher vents were more explosive, with strombolian activity, while the lower vents were more effusive. Accordingly, most of the lava (~8×10⁷ m³ in 1999 and ~6×10⁶ m³ in 2000) was emitted from the lower sites. The 1999–2000 lavas are predominantly basanites with low Ni (5–79 ppm), Cr (40–161 ppm) and mg numbers (34–40). Olivine (Fo_77–85, phenocrysts and Fo_68–72, microlites), clinopyroxene (Wo₄₇En₄₁Fs₁₀ to Wo₅₁En₃₄Fs₁₅), plagioclase (An_49–67) and titanomagnetite are the principal phenocryst and groundmass phases. The lavas contain xenocrysts of olivine and clinopyroxene, which are interpreted as fragments of intrusive rocks disrupted by magma ascent. Major and trace element characteristics point to early fractionation of olivine. The clinopyroxenes (Al₂O₃ 1.36–7.83 wt%) have high Al^iv/Al^vi ratios (1.3–1.8) and are rich in TiO₂, characteristics typical of low pressure clinopyroxenes. Geochemical differences between the 1999–2000 lavas and those from previous eruptions, such as higher Nb/Zr of the former, suggest that different eruptions discharged magmas that evolved differently in space and time. Geophysical and petrological data indicate that these fractionated magmas originated just below the geophysical Moho (at 20–22 km) in the lithospheric mantle. During ascent, the magmas disrupted intrusions and earlier magma pockets. The main ascent path is below the summit, where newly arrived magma degasses. Degassed magma simultaneously intrudes the flank rift zones where most lava is extruded.An erratum to this article can be found at     

Seismic quantification of the explosions that destroyed the dome of Volcán de Colima, Mexico, in July–August 2003

In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×10⁶ m³ dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×10¹¹ N and 1×10¹¹ N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions.     

Magma fragmentation dynamics: experiments with analogue porous low-strength material

 Experiments were conducted on the fragmentation of analogue low-strength porous material (plastiprin) by rapid decompression in a shock-tube-type apparatus. The porous samples (length=365 mm, cross-section dimensions 40×40 mm) pressurized by air to pressures up to 0.9 MPa, were rapidly decompressed to 0.1 MPa. Rapid decompression of samples caused fragmentation and ejection of the fragmentation products into a large volume tank. The process of analogue material fragmentation was documented using high-speed cinematography and dynamic pressure measurements. The duration of the fragmentation event is significantly shorter than that of the ejection event. The fragmentation of material precedes the acceleration of fragments. As a result of fragmentation, sub-parallel fractures are generated. The characteristic fragment size decreases as the initial pressure differential increases. The ejected fragments obtain velocities of 60 m/s. The mechanisms of material fragmentation during unloading and fragmentation wave propagation are discussed. The experimental results provide insight into the fragmentation dynamics of highly viscous magmas in which brittle failure at high strain rate is possible. Received: 23 July 1997 / Accepted: 23 November 1997     

The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types

The eruptive history of the Tequila volcanic field (1600 km²) in the western Trans-Mexican Volcanic Belt is based on ⁴⁰Ar/³⁹Ar chronology and volume estimates for eruptive units younger than 1 Ma. Ages are reported for 49 volcanic units, including Volcán Tequila (an andesitic stratovolcano) and peripheral domes, flows, and scoria cones. Volumes of volcanic units 1 Ma were obtained with the aid of field mapping, ortho aerial photographs, digital elevation models (DEMs), and ArcGIS software. Between 1120 and 200 kyrs ago, a bimodal distribution of rhyolite (~35 km³) and high-Ti basalt (~39 km³) dominated the volcanic field. Between 685 and 225 kyrs ago, less than 3 km³ of andesite and dacite erupted from more than 15 isolated vents; these lavas are crystal-poor and show little evidence of storage in an upper crustal chamber. Approximately 200 kyr ago, ~31 km³ of andesite erupted to form the stratocone of Volcán Tequila. The phenocryst assemblage of these lavas suggests storage within a chamber at ~2–3 km depth. After a hiatus of ~110 kyrs, ~15 km³ of andesite erupted along the W and SE flanks of Volcán Tequila at ~90 ka, most likely from a second, discrete magma chamber located at ~5–6 km depth. The youngest volcanic feature (~60 ka) is the small andesitic volcano Cerro Tomasillo (~2 km³). Over the last 1 Myr, a total of 128±22 km³ of lava erupted in the Tequila volcanic field, leading to an average eruption rate of ~0.13 km³/kyr. This volume erupted over ~1600 km², leading to an average lava accumulation rate of ~8 cm/kyr. The relative proportions of lava types are ~22–43% basalt, ~0.4–1% basaltic andesite, ~29–54% andesite, ~2–3% dacite, and ~18–40% rhyolite. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, textures, and chemical composition, the lavas do not reflect the differentiation of a single (or only a few) parental liquids in a long-lived magma chamber. The rhyolites are geochemically diverse and were likely formed by episodic partial melting of upper crustal rocks in response to emplacement of basalts. There are no examples of mingled rhyolitic and basaltic magmas. Whatever mechanism is invoked to explain the generation of andesite at the Tequila volcanic field, it must be consistent with a dominantly bimodal distribution of high-Ti basalt and rhyolite for an 800 kyr interval beginning ~1 Ma, which abruptly switched to punctuated bursts of predominantly andesitic volcanism over the last 200 kyrs.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial responsility: J. Donnelly-NolanThis revised version was published online in January 2005 with corrections to Tables 1 and 3.An erratum to this article can be found at     

Hawaii bibliographic database

 The Hawaii bibliographic database has been created to contain all of the literature, from 1779 to the present, pertinent to the volcanological history of the Hawaiian-Emperor volcanic chain. References are entered in a PC- and Macintosh-compatible EndNote Plus bibliographic database with keywords and abstracts or (if no abstract) with annotations as to content. Keywords emphasize location, discipline, process, identification of new chemical data or age determinations, and type of publication. The database is updated approximately three times a year and is available to upload from an ftp site. The bibliography contained 8460 references at the time this paper was submitted for publication. Use of the database greatly enhances the power and completeness of library searches for anyone interested in Hawaiian volcanism. Received: 1 June 1997 / Accepted: 17 September 1997     

腾冲火山岩年龄问题评述

腾冲火山及火山岩是国内新近纪火山及其喷发物九大分布区之一,研究程度较广较深,喷发序列岩石定岩及年龄值资料丰富,综合评述并指出今后研究方向。     

Precursory seismicity of the 1994 eruption of Popocatépetl Volcano,Central Mexico

Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over 20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions, including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime, the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes, limit that was reached by Popocatépetl before the eruption.