The Colima Volcanic complex,Mexico

Volcán Colima is Mexico's most historically active andesitic composite volcano. It lies 150 km north of the Middle America Trench at the western end of the Mexican Volcanic Belt, closer to the trench than any other composite volcano in Mexico. Since its earliest reported eruption in 1576, V. Colima has evolved through three cycles of activity. Each cycle culminated in a major ashflow eruption, halting activity for 50 or more years. The last major ashflow eruption occurred in 1913. Andesitic block lava eruptions in 1961–1962 and 1975–1976 marked the inception of activity in a fourth historical cycle which may also terminate with a major ashflow eruption in the early part of the next century.Major and trace element analyses of whole rock samples and all constituent phases are presented for a suite of nine post-caldera hornblende and olivine-andesites. The suite includes samples from Colima's four major eruptions since 1869, spanning the last two eruptive cycles. Colima's post-caldera andesites are poor in K and other incompatible elements (Ti, P, Zn, Rb, Y, Zr, Ba, La, Yb, Hf, Th, and U) as may be characteristic of near trench andesites. From the 1913 ashflow eruption through the fourth cycle andesites, there have been increases in whole rock abundances of Si, Ba, and Cs, and decreases in Ti, Fe, Mg, Ni, Cr, and Sc. Crystal fractionation models can closely reproduce major element variations in the post-caldera suite, but systematically fail to predict sufficient concentrations of the compatible trace elements Cr, Ni, and Zn. Anomalous enrichments of compatible trace elements in Colima's andesites probably reflect simultaneous crystal fractionation and magma mixing in the subvolcanic system.Estimated pre-eruptive temperatures range from 940 °–1,000 ° C in the hornblende-andesites and 1,030 °–1,060 ° C in the olivine-andesites. Pre-eruptive magmatic water contents of 1.0–3.6 wt.% are calculated for the hornblende-andesites; the phenocryst assemblage of the olivine-andesite is calculated to equilibrate at 1,000 bars with 0.8% H₂O.Orthopyroxenes and certain clinopyroxenes in all pre-1961 samples are reversely zoned, with relatively Mg-rich rims. The most pronounced Mg-rich rims occur in the olivine-andesites and are thought to reflect pre-eruptive magma mixing, involving a basic, olivine+/-clinopyroxene-bearing magma. In addition to their normally zoned pyroxenes, the post-1961, fourth cycle andesites display a number of other features which distinguish them from earlier post-caldera hornblende-andesites of similar bulk composition. These include: (1) higher total crystal contents, (2) lower modal hornblende contents, (3) higher calculated pre-eruptive silica activities, and (4) lower calculated pre-eruptive water contents. These features are all consistent with the interpretation that the fourth cycle andesites were less hydrous prior to eruption. The slight Mg-rich pyroxene rims in pre-1961 hornblende-andesites may record late-stage, pre-eruptive increases in magmatic water content, which act to raise magmatic f _{O 2} and Mg/Fe⁺² ratios in the melt and in all crystalline phases. The fourth cycle andesites apparently did not experience a strong, pre-eruptive influx of water, resulting in lower magmatic water contents and normally zoned pyroxenes.     

Lamprophyric lavas in the Colima graben,SW Mexico

The Colima graben, located in SW Mexico, is one of three grabens which intersect about 50 km SSW of Guadalajara, forming a triple junction. The 90 km long, 20–60 km wide Colima graben represents a N-S rift of the E-W trending Mexican Volcanic Belt. Since the Early Pliocene, the Colima graben has served as a locus for the eruption of alkaline lavas, the most recent of which are basanites and minettes erupted from Late Pleistocene cinder cones (Luhr and Carmichael 1981). In this paper, we report on older alkaline lavas which crop out in the graben's walls. These rocks include phlogopite- and hornblende-bearing lamprophyres, a phlogopite-kalsilite-ankaratrite, and high-K andesites. These lavas crop out throughout the Colima graben area, and are intimately associated with calc-alkaline lavas in the field. Compared to these, the alkaline rocks are strikingly enriched in the incompatible elements, particularly Ba, Sr, P, and the LREE. Unlike the younger Late Pleistocene alkaline cinder cone lavas, most of the graben wall lamprophyres and the high-K andesites represent magmas that appear to have undergone significant evolution since their generation, including fractionation, crustal contamination, and possible magma mixing. Least-squares modeling indicates that the cinder cone minettes represent reasonable parental magmas for the graben lamprophyres. The occurrence of these alkaline lavas in an active calc-alkaline volcanic arc is unusual, and we suggest that they are a manifestation of the rifting processes which produced the Colima graben.     

Volcanic hazards zonation of the Nevado de Toluca Volcano,Central Mexico

Nevado de Toluca Volcano (NTV), located in central Mexico, is a large stratovolcano, with an explosive history. The area is one of the most important developing centers (>2 millions) in Mexico and in the last 30 yrs large population growth and expansion have increased the potential risk in case of a reactivation of the volcano. As part of a study to assess volcanic risk, this paper presents the results of the volcanic hazard analysis for the NTV. A total of 150 stratigraphic sections were made in the field and three new ages were obtained. Eruptions from NTV produced a complex sequence of pyroclastic deposits that have affected the area at least 18 times during the last 100,000 yrs. Eight vulcanian, four plinian and one-ultraplinian eruptions as well as the destruction of at least three domes occurred in the last 42,000 yr BP as well as two sector collapses in the last 100,000 yrs. Isopach and isopleth maps for the main ulraplinian eruption were also made. The original cone height (5,080 m.a.s.l) was reconstructed through geomorphologic methods. The maximum distance calculated with the energy line for the block and ash flows was 41 km, 35 km for pumice flows and 45 km for debris avalanches. The dominant wind direction at altitudes of 20–30 km is to the east-northeast from November to March, west-northwest in April and west from May to October. Five hazards maps (block and ash flows, pumice flows, ash fall, debris avalanches, and lahars) were made for the NTV. The pyroclastic flows and lahars represent very high to medium hazard for Toluca, Villa Guerrero, Coatepec, Tianguistengo, Metepec, Tenango, Lerma and Zinacantepec. A new debris avalanche would probably affect the south and northeast because of active faulting (E–W and NW–SE) and existing topographic differences in height.     

The Colima volcanic complex,Mexico: Part II. Late-quaternary cinder cones

Since the late Pleistocene, eleven cinder and lava cones have erupted on the floor of the southern Colima graben, NE and NW of the large, active, andesitic volcano Colima. Scoria and lava samples from nine of the cones form a completely transitional basic alkalic series including basanites (9), leucite-basanites (3), and minettes (15), the commonest variety of mica lamprophyre. These samples represent primitive, high temperature magmas with 47.6–50.3% SiO₂, 7.4–15.3% MgO, 2.5–4.4% K₂O, and 2.2–9.9% normative nepheline. All members of this basic alkalic suite contain Mg-olivine (Fo_75–94), chromite, augite, and late plagioclase and titanomagnetite. The petrographic transition from basanite to minette is marked by the appearance of sanidine and the volatile-bearing phases phlogopite, apatite, and analcime during late stages of crystallization. As these phases increase in abundance, presumably reflecting a rise in magmatic volatile content, there are corresponding increases in the whole rock concentrations of 16 incompatible elements. Although these incompatible elements are relatively abundant even in the basanites, many are highly concentrated in the minettes: Ba 4,200 ppm, Sr3,100 ppm, Zr 550 ppm, Ce190 ppm, Hf 18 ppm. Among the incompatible elements, the degrees of enrichment in the minettes relative to the basanites decrease in the order: H, Th, Ce, La, Nd, Zr, Hf, U, Ba, Sm, Eu, Pb, P, Nb, Sr, Ti. These enrichments may reflect the increasing importance of minor, incompatible element rich mantle phases during partial melting. The concentrations of alkali metals K, Na, Rb, and Cs do not correlate with these other elemental enrichments. The leucite-basanties have similar incompatible element contents to many minettes, differing from them only in the presence of leucite rather than analcime, and Ti-F-rich groundmass phlogopite rather than hydrous phlogopite phenocrysts; thus the leucite-basanites represent relatively dry equivalents of minettes.Two of the eleven cinder cones are calc-alkaline in nature and do not belong to the basanite-minette group; the easternmost cone is constructed of high-Al basalt, and the northernmost of basaltic andesite. The high-Al basalt (49.5% SiO₂, 9.3% MgO, 221 ppm Ni) closely approximates a parental magma to the post-caldera andesitic suite of V. Colima (56.5–61.6% SiO₂). The basaltic-andesite is relatively enriched in incompatible elements compared to the high-Al basalt — V. Colima trend.The ne-normative basanite-minette samples are highly enriched in incompatible elements, while the contemporaneous hy — qz-normative calc-alkaline suite, encompassing the high-Al basalt and V. Colima's andesites, is characterized by relatively low abundances of these elements. No likely mineral assemblage can relate the alkaline and calc-alkaline suites through crystal fractionation; they probably represent fundamentally different melting events.During the Quaternary, the main focus of andesitic volcanism in the southern Colima graben has migrated southward with time. Volcán Colima marks its present position, 5 km south of the Pleistocene volcano Nevado de Colima, and another 15 km from the still older Volcán Cantaro. The eruptions of basic alkalic magma probably occurred during the late stages of Nevado's life and through the life of V. Colima. They generally migrated from west to east with time, towards V. Cantaro. The most recent cone, V. Apaxtepec, is the only one east of the andesitic Colima-Cantaro axis. The oldest and the two youngest cones produced basanites, while minettes dominated at cones of intermediate ages. The cinder cone eruptions may have coincided with a phase of lamprophyre dike injection into plutons solidifying beneath the extinct volcanoes north of V. Colima. The southern end of the Colima graben can be viewed, then, as the volcanic analog of many classical, post-plutonic, hypabyssal lamprophyre localities.     

Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr

Many years of low growth identified in a western USA regional chronology of upper forest border bristlecone pine (Pinus longaeva and Pinus aristata) over the last 5000 yr coincide with known large explosive volcanic eruptions and/or ice core signals of past eruptions. Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases. In previous millennia, while there is substantial concurrence, the agreement decreases with increasing antiquity. Many of the bristlecone pine ring-width minima occurred at the same time as ring-width minima in high latitude trees from northwestern Siberia and/or northern Finland over the past 4000-5000 yr, suggesting climatically-effective events of at least hemispheric scale. In contrast with the ice-core records, the agreement between widely separated tree-ring records does not decrease with increasing antiquity. These data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees, and they augment the ice core record in a number of ways: by providing confirmation from an alternative proxy record for volcanic signals, by suggesting alternative dates for eruptions, and by adding to the list of years when volcanic events of global significance were likely, including the mid-2nd-millennium BC eruption of Thera.     

Tephra Discovered in High Resolution Peat Sediment and Its Indication to Climatic Event

Floating tephra was deposited together with ice core,snow layer,abyssal sediment,lake sediments,and other geological records.It is of great significance to interpret the impact on the climate change of volcanic eruptions from these geological records.It is the first time that volcanic glass was discovered from the peat of Jinchuan(金川)Maar,Jilin(吉林)Province,China.And it is in situ sediments from a near-source explosive eruption according to particle size analysis and identification results.The tephra were neither from Tianchi(天池)volcano eruptions,Changbai(长白)Mountain,nor from Jinlongdingzi(金龙顶子)volcano about 1 600 aBP eruption,but maybe from an unknown eruption of Longgang(龙岗)volcano group according to their geochemistry and distribution.Geochemical characters of the tephra are similar to those of Jingiongdingzi,which are poor in s.Jica,deficient in alkali,Na20 content is more than K20 content,and are similar to distribution patterns of REE and incompatible elements,which helps to speculate that they originated from the same mantle magma with rare condemnation,and from basaltic explosive eruption of Longgang volcano group.The tephra,from peat with age proved that the eruption possibly happened in 15 BC-26 AD,is one of Longgang volcano group eruption that was not recorded and is earlier than that of Jinglongdingzi about 1 600 aBP eruption.And the sedimentary time of tephra is during the period of low temperature alteration.which may be the influence of eruption toward the local climate according to the correlativity of eruption to local temperature curve of peat cellulose oxygen isotope.     

Pre‐Holocene age of Humboldt's 1430 eruption of the Orotava Valley,Tenerife, Canary Islands

Errors in the interpretation of clouds, fumarolic activity and forest fires as volcanic eruptions in Tenerife, mainly in relation with Teide volcano, are common in references by passing navigators and other eyewitness accounts from the fifteenth and sixteenth centuries. In the case of the most common, historical, multiple‐vent fissure eruptions in the Canaries, vent locations provided by these accounts are frequently uncertain or are clearly erroneous and often conflict with geological evidence. Significant examples are the general association of the latest eruption of Teide volcano, dated at 1150 ± 140 bp , with the reference made by Christopher Columbus in 1492 to an eruption ‘on the flanks of Teide’, which actually corresponds to an eruptive vent (Boca Cangrejo volcano) situated in the NW Rift, dated at 400 ± 110 bp . Similar conflicting vent locations occurred in the 1730–36 eruption of Lanzarote and the 1677 eruption of La Palma. This article considers the volcanic cones located in the Orotava Valley, erroneously assigned by Chevalier de Borda and Alexander von Humboldt to a 1430 ad eruption. Geological evidence and radiocarbon dating of charcoal underlying the lapilli, and ⁴⁰Ar/³⁹Ar dating of one of the lava flows, show that these volcanic cones and lavas correspond to an eruption that took place about 30 000 yr bp . Analysis of the influence of these erroneous ages for the recent volcanism of Tenerife shows an overestimation of eruptive hazards of this island.     

The Colima volcanic complex,Mexico:III

A 34 meter section of ash- and scoria-fall units has been studied on the upper NE flank of the active Volcán Colima. Charcoal and soil horizons are restricted to the topmost 12 m. Nine ¹⁴C dates show a smooth progression from 235 years near the surface to 8,300 years at 10 meters depth, indicating a post-Pleistocene accumulation rate of 1.3 m/1,000 years at 6 km from the vent. This figure allows an estimate of the magmatic eruption rate for fallmaterial of 0.31 km³/1,000 years, less than 15% of Colima's lava eruption rate. An unusually thick and coarse-grained scoria-fall horizon at about 4 m depth in the section appears to have been produced by the caldera-forming eruption of Colima some 4,300 years ago.The majority (40) of 46 analyzed scoria and ash horizons are typical Colima hornblende-andesites with an average SiO₂ content of 58%, nearly identical to the scoriae of Colima's 1913 pyroclastic flows. The scoriae are significantly more basic than Colima's andesitic lavas, which average 61% SiO₂. The six remaining scoria horizons are anomalously alkalic and rich in incompatible elements. Five coarse alkaline scoria layers occur in sequence just below the 8,300 year level. They show progressive upward increases in K, P, Ba, Sr, Zr, La, Ce, and related elements, culminating in a phlogopite-bearing scoria horizon.Over the last 20,000 years or so, a group of cinder cones erupted 20–35 km to the north of Volcán Colima, producing basic alkalic magmas including basanites and phlogopite-bearing minettes. The alkaline scoriae of the studied sections probably record pre-eruptive injections of minette magma into the subvolcanic, calc-alkaline system of V. Colima. The age, composition, and mineralogy of the alkaline scoriae are consistent with this interpretation. Least squares mixing models suggest 60 wt.% minette component in the phlogopite-bearing horizon.     

A 2.5 ka History of Dacitic Magmatism at Nevado de Toluca, Mexico: Petrological, 40Ar/39Ar Dating, and Experimental Constraints on Petrogenesis

After 11·5 ka of quiescence (24·5–13 ka),the Nevado de Toluca volcano started a 2500 year period of activity.This period was characterized by a dome destruction event at13 ka, a small Plinian event at 12·1 ka, and a largePlinian eruption at 10·5 ka. About 10 km³ of magma waserupted that was homogeneous in composition (63·3–65·7SiO₂ wt % whole-rock) and in mineralogy. Pumice consists ofplagioclase (An_30–59) > orthopyroxene (En_56–59)> hornblende >> Fe–Ti oxides + rare apatite (inopx) + biotite, set in a rhyolitic matrix (72–76 SiO₂wt %). ⁴⁰Ar/³⁹Ar analysis of single biotite crystals yieldedages (0·81–4·7 Ma), that do not correspondto eruption ages. The biotite represents partially assimilatedxenocrysts, which could have resided in the magma for only ashort period of time. Mineral chemical data, coupled with hydrothermalexperiments, indicate that prior to eruption the dacitic magmastagnated at a depth of 4·5–6 km below the summitat water pressures of 160–210 MPa and a temperature of824 ± 12°C on the basis of Fe–Ti oxide thermometry,and under water-saturated conditions. To stabilize a homogeneousmagma body of >10 km³ at 824°C in the upper crust, wepropose that reheating of the dacitic reservoir by hotter magmabatches was able to maintain the equilibrium between the temperatureof the magma and the assimilation of wall-rock over a periodof 2500 years. Based on similarities among the juvenile products,we suggest that the three eruptions were fed from the same magmabody. KEY WORDS: explosive volcanism; xenocrystic contamination; Nevado de Toluca, Mexico     

From sink to volcanic source: Unravelling missing terrestrial eruption records by characterization and high‐resolution chronology of lacustrine volcanic density flow deposits,Lake Inawashiro‐ko,Fukushima, Japan

Eruption records in the terrestrial stratigraphy are often incomplete due to erosion after tephra deposition, limited exposure and lack of precise dating owing to discontinuity of strata. A lake system and sequence adjacent to active volcanoes can record various volcanic events such as explosive eruptions and subaqueous density flows being extensions of eruption triggered and secondary triggered lahars. A lacustrine environment can constrain precise ages of such events because of constant and continuous background sedimentation. A total of 71 subaqueous density flow deposits in a 28 m long core from Lake Inawashiro‐ko reveals missing terrestrial volcanic activity at Adatara and Bandai volcanoes during the past 50 kyr. Sedimentary facies, colour, grain size, petrography, clay mineralogy, micro X‐ray fluorescence analysis and chemistry of included glass shards characterize the flow event deposits and clarify their origin: (i) clay‐rich grey hyperpycnites, extended from subaerial cohesive lahars at Adatara volcano, with sulphide/sulphate minerals and high sulphur content which point to a source from hydrothermally altered material ejected by phreatic eruptions; and (ii) clay‐rich brown density flow deposits, induced by magmatic hydrothermal eruptions and associated edifice collapse at Bandai volcano, with the common presence of fresh juvenile glass shards and low‐grade hydrothermally altered minerals; whereas (iii) non‐volcanic turbidites are limited to the oldest large slope failure and the 2011 Tohoku‐oki earthquake events. The high‐resolution chronology of volcanic activity during the last 50 kyr expressed by lacustrine event deposits shows that phreatic eruption frequency at Adatara has roughly tripled and explosive eruptions at Bandai have increased by ca 50%. These results challenge hikers, ski‐fields and downstream communities to re‐evaluate the increased volcanic risks from more frequent eruptions and far‐reaching lahars, and demonstrate the utility of lahar and lacustrine volcanic density flow deposits to unravel missing terrestrial eruption records, otherwise the recurrence rate may be underestimated at many volcanoes.     

Risk assessment for the Yucca Mountain high-level nuclear waste repository site: Estimation of volcanic disruption

In this article, we model the volcanism near the proposed nuclear waste repository at Yucca Mountain, Nevada, U.S.A. by estimating the instantaneous recurrence rate using a nonhomogeneous Poisson process with Weibull intensity and by using a homogeneous Poisson process to predict future eruptions. We then quantify the probability that any single eruption is disruptive in terms of a (prior) probability distribution, since not every eruption would result in disruption of the repository. Bayesian analysis is performed to evaluate the volcanic risk. Based on the Quaternary data, a 90% confidence interval for the instantaneous recurrence rate near the Yucca Mountain site is (1.85×10^–6/yr, 1.26×10^–5/yr). Also, using-these confidence bounds, the corresponding 90% confidence interval for the risk (probability of at least one disruptive eruption) for an isolation time of 10⁴ years is (1.0×10^–3, 6.7×10^–3), if it is assumed that the intensity remains constant during the projected time frame.     

Age and significance of the Late Pleistocene Dawson tephra in eastern Beringia

Dawson tephra, recently recognized in the Klondike area of Yukon Territory, records one of the largest Quaternary volcanic eruptions in Beringia. Its composition is similar to that of Old Crow tephra, indicating a source in the Aleutian arc-Alaska Peninsula region of southwestern Alaska. Its primary thickness in central Yukon is nearly twice that of Old Crow tephra, which has an estimated eruption volume of >50 km³. The distribution of Dawson tephra is still poorly known, but based on its source area and occurrence in central Yukon, it should be widespread across southern Alaska, Yukon and the Gulf of Alaska. New radiocarbon ages indicate the eruption occurred at about 24,000 ¹⁴C yr BP (ca 27,000 cal yr BP). The Dawson tephra is a valuable marker bed for correlating late Pleistocene records across large areas of eastern Beringia and adjacent marine records.     

Volcanic eruptions in the Longgang volcanic field,northeastern China,during the past 15,000 years

The Longgang volcanic field, located in northeastern China, is volcanically active with a number of eruptions during the Quaternary but the chronology of the eruptions is poorly defined. Some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region, and facilitate the construction of a much improved chronological framework for the volcanic history of the area. The results of our investigations reveal that three basaltic explosive eruptions occurred at AD 460, 11460 cal yr BP and 14000 cal yr BP, respectively. The largest explosive basaltic eruption (AD 460) produced a thick black scoria layer in the Longgang volcanic field, including lakes. The tephra distribution and chronological data suggest that this eruption is likely to be from the Jinlongdingzi volcano. Two basaltic flood eruptions occurred at Jinlongdingzi. The earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees. Two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828–1989 cal yr BP and 2164–2359 cal yr BP. In the most recent stage of volcanism, the lava flow extended only ca. 2 km, and flowed into Lake Dalongwan. From the present status of the forest ecosystem, which has not yet reached the fully mature successional stage, we estimate that this lava is very young (ca. a few hundreds years old). Jinlongdingzi is a potentially dangerous volcano. Monitoring and assessment of the potential hazards in the Longgang volcanic field should be carried out in the future.     

Volcanic threat in developing countries of the Asia�CPacific region: probabilistic hazard assessment, population risks, and information gaps

The importance of disaster reduction has gained increased awareness within the international development community and thereby highlighted a need for a preliminary assessment of natural hazard risk in developing countries of the Asia?CPacific, including that for volcanic eruption. In this paper, we present a key component of such an assessment, which involved qualifying the frequency and potential consequences of large??Volcanic Explosivity Index of four or more??volcanic eruptions. The frequencies of large eruptions from volcanoes grouped by region were determined from frequency?Cmagnitude plots using data provided by the Smithsonian Institution??s Global Volcanism Program. However, calculated frequencies represent only minimum values due to an incomplete eruption record. Unfortunately, limited data precluded the calculation of eruption frequencies for the Solomon Islands, Fiji and Samoa. A first-order analysis of the populations potentially impacted by large volcanic eruptions suggest that (1) volcanic disasters affecting populations of >100,000 can be expected at least every decade in Indonesia and once every few decades in the Philippines and (2) a volcanic disaster impacting >1% of the population can be expected twice a century in Vanuatu, twice a millennium for Indonesia and the Philippines, and around every millennium in Papua New Guinea and Tonga.     

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.     

A significant aegean volcanic eruption during the second millennium B.C. revealed by thermoluminescence dating

Thermoluminescence dating of four volcanic samples (material of eruption ejecta), from the island of Yiali near the Nissyros volcano in the southeastern Aegean sea, Greece, has revealed, for first time, a volcanic eruption which occurred during the 2nd millennium B.C. (c. 1460 B.C.), different from the known Santorini eruption. The interrelation between Yiali and the well-known Santorini eruption, as well as the implications of these eruptions regarding their potential impact to the Aegean prehistoric archaeology (demise of the Minoan civilization), are discussed. © 1996 John Wiley & Sons, Inc.     

Study on the Relationship between Large Volcanic Eruptions and Temperature Variation Based on Tree-Ring Data in the Eastern Tibetan Plateau during the Past Millennium

Volcanic eruptions can significantly cool the global troposphere on the time scales from several months up to a decade due to reflection of solar radiation by sulfate aerosols and feedback mechanisms in the climate system. The impact of volcanic eruptions on global climate are discussed in many studies. However, few studies have been done on the impact of volcanic eruption on climate change in China in the past millennium. The 1300-year and 600-year temperature series were reconstructed based on the six tree-ring temperature proxy data in northeastern and southeastern Tibetan Plateau, respectively. Three warm periods occurred in 670-920,1000-1310 and 1590-1930, and three cold periods happened at 920-1000,1310-1590 and 1930-2000 in the northeastern Tibetan Plateau. There were two obviously warm periods (1385-1450 and 1570-1820) and two cold periods (1450-1570 and 1820-2000) in southeastern Tibetan Plateau. Contrasting with volcanic eruption chronology, we analyzed the relationship between volcanic activity and temperature variation in the eastern Tibetan plateau during the past millennium using Superposed Epoch Analysis (SEA) method. The results indicated that the temperature decreased one year after large volcanic eruptions located beteen 10°S and 10°N in latitude in northeastern Tibetan Plateau and two years in southeastern Tibetan Plateau. The volcanic eruptions occurred at different latitudes have different impacts on the temperature variations, which may be caused by regional difference, the nature of the eruption, the magnitude of the resulting change in incoming solar radiation, prevailing background climate and internal variability, season, latitude, and other considerations.     

New records of late Holocene tephras from Lake Futalaufquen (42.8°S), northern Patagonia

In regions with limited knowledge of the historical volcanic record, like remote areas in the Andean Southern Volcanic Zone, the definition of reliable age-depth models for lake sequences represents a valuable tool for tephra layers dating. In Lake Futalaufquen (42.8°S), Northern Patagonia, a short sedimentary sequence was extracted after the AD 2008 Chaitén eruption with the purpose to analyze the records of volcanic eruptions at these poorly studied latitudes. The sequence was dated by ²¹⁰Pb, ¹³⁷Cs, and ¹⁴C techniques. Five tephras were identified for the last 1600 years, restricted to the last 5 centuries. Sedimentology, morphology, and geochemical properties allowed the characterization of the tephras and their correlation with tephras recently identified proximal to the sources, mainly from Chaitén and Huequi volcanoes, and Michinmahuida accessory cones, representing the first distal records reported of these tephras. Furthermore, tephras modeled ages obtained by the sequence age-depth model shrink the ages for the volcanic events, like a potential cycle of activity from Michinmauida accessory cones during AD 1530 ± 55, one eruption from Huequi volcano at AD 1695 ± 50, and a possible recent eruption from Chaitén at AD 1775 ± 40. Additionally, the work contributes to improve the regional volcanic records knowledge, basic for volcanic hazard assessment.     

天文因素对火山爆发的调制、触发作用

本文分析得到:1957—1982年间,全球低纬度火山爆发有73.9％和高纬度火山爆发有62.5％,分别发生在地球自转年际变化的减速段和加速段;火山爆发的日期,一般多发生在3天内遇到3个以上天文奇点引潮力共振加压的叠加之时,强火山爆发都发生在4个以上此种共振加压之时。表明地球自转速度变化和天文奇点引潮力共振加压在不同时间尺度上,分别对火山爆发具有调制和触发作用。其物理机理,两者都是引起火山附近地壳异常加压,促使岩浆受到挤压而累积能量或触发爆发。     

火山活动与气候变化研究进展

综述了火山活动对气候影响的研究进展。不同岩浆成分及喷发类型的火山活动对气候的影响不同：中酸性普林尼（Pl inian）式火山喷发主要造成气候变冷和臭氧层破坏，它导致气候变化的时间较短，但空间范围较大；大火成岩省造成气候变化的时空范围及程度均较大，它能够导致地表温度、海平面大幅度变化，最终引起生物灭绝；中小规模玄武质裂隙式喷发主要造成火山盆地内气候较大幅度变化，但对气候影响的持续时间较短，主要气候效应是导致附近地区温度快速下降和形成酸雨。简要阐述了第四纪火山活动的特点。