a reappraisal of the 1835 eruption of cosiguina and its atmospheric impact in the great january 1835 eruption of cosiguina volcano nicaragua andesitic magma and lithic material were erupted over a period of at least three days proximal facies consist of clastogenic lava scoria fall and lithic ash fall produced by phreatomagmatic to vulcanian or plinian activity together with surge deposits and lithic block falls pyroclastic flow deposits covered some flanks of the volcano and entered the sea in the gulf of fonseca little record exists of the distal ash fall thus the total bulk volume erupted can only be roughly constrained to 2 9 5 6 km3 furthermore the amount of juvenile material is thought to be small a recent study of volatiles in 1835 scoria suggests sulfur release from the magma was negligible this reappraisal indicates that the cosiguina eruption probably had little global climatic impact despite its violent nature the magnitude of the eruption was modest the eruption occurred too late to initiate the northern hemisphere cooling trend form 1828 1836 dry fogs and other atmospheric optical phenomena usually observed after eruptions that contribute significantly to the stratospheric aerosol burden were not recorded after 1835

a continuous 770 year record of volcanic activity from east antarctica a 100 m ice core from site g 15 accumulation rate 0 1 m water yr 1 mean annual temperature 38 c on the mizuho plateau dronning maud land east antarctica has been analysed using the dielectric profiling dep technique the capacitance and conductance of the core were measured at ac frequencies 20 hz 300 khz the high frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity the tambora 1815 eruption can be identified with the aid of an approximate chronology based on the firn densification rate other historic eruptions can then be recognised beyond about 300 years historical observations are very few however if a constant overall accumulation rate is assumed a well known eruption of 1259 a d can be found near the bottom of the core other peaks in the conductivity profile can then be assigned dates accurate to within a few years using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy the estimated acid deposisition fluxes realtive to the tambora 1815 eruption of agung 1963 is 27 krakatoa 1883 25 the signal of 1601 28 and that of 1259 53

tree ring evidence of the widespread effects of explosive volcanic eruptions tree ring evidence from 97 sites over north america and europe are used to develop a chronology of widespread cool summers since 1600 averaging annual maximum density information from the chronologies provides an index that correlates with northern hemisphere summer temperatures to 0 44 over 1851 1975 a number of the extreme low density years occur in both north america and europe suggesting a common response to high frequency forcing the analysis was repeated with ring width information but the results are markedly less coherent of the five common extreme low density years 1601 1641 1669 1699 and 1912 four are known to be coincident with the year or year following major volcanic eruptions other extreme low density indices in the continental series are also clear coincident with known volcanoes the density indices clearly demonstrate great potential for quantifying the climate effectiveness and perhaps establishing precise calendar dates of large explosive volcanoes 30 refs

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

glaciological studies at siple station antarctica potential ice core paleoclimatic record the quality and utility of the records of oxygen isotopic abundances dust concentrations and anionic concentrations preserved in the ice at siple station 75 55 s 84 15 w are assessed from four shallow 20 m cores the combination of high accumulation 0 56 m a 1 w e and low mean annual temperature 24 c preserves the prominent seasonal variations in 18 which are very spatially coherent sulfate concentrations vary seasonally and in conjunction with 18 will allow accurate dating of deeper cores from siple station the concentrations of insoluble dust are the lowest measured in antarctica making siple station an excellent location to examine large increases in atmospheric tubidity the seasonal variations and annual fluxes of the anions are examined for the last two decades ad 1966 85 with regard to probable sources an unusually high sulfate flux in 1976 may reflect the february 1975 eruption of mount ngauruhoe new zealand no annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares however nitrate flux is higher for the latter half of the 1970s and early 1980s possibly reflecting the recent loss of stratospheric ozone finally comparison of the 18 o record with available surface temperature data ad 1957 85 reveals that multi year trends along the western coast of the antarctic peninsula are recorded at siple more importantly comparison with areally weighted temperature reconstructions suggests that the 18 record may reflect larger scale persistent trends in the high southern latitudes the strong spatial coherence of the preserved records the potential for accurate dating and possible relevance to larger scale processes make siple station an excellent site for paleoenvironmental reconstruction from ice cores

kuwae 1425 a d the forgotten caldera in vanuatu tongoa and epi islands once formed part of a larger landmass kuwae which was partly destroyed during a cataclysmic seismo volcanic event that is recorded in local folklore it led to the formation of a 12 kmlong and 6 km wide oval shaped submarine caldera with two distinct basins and a total area of 60 km2 at the level of the rim the age ofthis eniption 1420 1430 a d and the structure of the related collapse are discussed and a composite log 143 m of the pyroclastics surrounding the caldera is presented they comprise thick hydromagmatic deposits belonging to a terminal hydromagmatic phase of the pre caldera edifice which grade upwards into two major sequences of pyroclastic flow deposits clearly related to the caldera event collapse near the caldera edge was at least in the range 650 to 950 m and may have been as much as 800 to 1100 m the volume of rocks engulfed during the caldera formation is 32 39 km3 suggesting the same volume of magma was erupted even if two coalescent collapse structures were formed it is worth noting that the kuwae caldera is not a reactivated structure but the result of a single event of short duration which occurred in the first half of the fifteenth century this event is one of the seven biggest caldera forming events during the last 10 000 years and is comparable with the santorini minoan eruption and the crater lake eruption

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

historic eruptions of tambora 1815 krakatau 1883 and agung 1963 their stratospheric aerosols and climatic impact abstract decreases in surface temperatures after the eruptions of tambora 1815 krakatau 1883 and agung 1963 were of similar magnitude even though the amount of material dust and volatiles injected into the stratosphere by these three events differed greatly large amounts of fine ash and volatiles were dispersed into the upper atmosphere by krakatau and tambora the agung eruption in 1963 was a much smaller vulcanian type eruption which injected dust and volatiles into the stratospheric aerosol layer more directly analyses of magmatic volatiles indicate that the agung eruption was proportionately richer in so 2 and cl than either tambora or krakatau relative amounts of fine ash produced by the tambora krakatau and agung eruptions are estimated at about 150 20 1 whereas the masses of atmospheric sulfate aerosols produced were on the order of 7 5 3 1 decreases in surface temperature of a few tenths of a degree c for several years following volcanic eruptions are primarily a result of the sulfate aerosols rather than of the silicate dust the similarity in the atmospheric response after these three eruptions supports the idea of limiting mechanisms on volcanic stratospheric aerosol loading which is suggested by microphysical processes of aerosol particles fluctuations in stratospheric aerosol optical depth seem to be controlled to a large degree by high intensity sulfur rich eruptions e g agung 1963 which may however be relatively small in total ejecta volume such eruptions leave little geologic record but appear as acidity peaks in polar ice cores

ice core evidence for an explosive tropical volcanic eruption 6 years preceding tambora high resolution analyses of ice cores from antarctica and greenland reveal an explosive volcanic eruption in the tropics in a d 1809 which is not reflected in the historical record a comparison in the same ice cores of the sulfate flux from the a d 1809 eruption to that from the tambora eruption a d 1815 indicates a near equatorial location and a magnitude roughly half that of tambora thus this event should be considered comparable to other eruptions producing large volumes ofsulfur rich gases such as coseguina krakatau agung and el chichtn the increase in the atmospheric concentration of sulfuric acid may have contributed to the northern hemisphere cooling observed in the early nineteenth century and may account partially for the decline in surface temperatures which preceded the eruption of tamborn in a d 1815

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

boundary layer roll statistics from sar the atmospheric boundary layer abl mean flow frequently consists of an organized secondary circulation in the form of counter rotating rolls embedded in it theory predicts this is the case for a range of thermodynamic conditions although generally associated with the formation of cloud streets numerical and theoretical studies suggest that rolls should be present whenever there is sufficient shear to organize the convection including cloud free conditions through their association with clouds and their modification of the mean low level flow abl rolls alter air sea interaction processes surface energy fluxes and the earth radiational balance despite their potential importance to climate there exist no prior studies that can establish the extent and statistical frequency of roll occurrence synthetic aperture radar sar can detect abl roll signature on the ocean surface a first regional climate scale attempt to construct abl roll frequency statistics from the radarsat sar observations is described

volcanic deposits in antarctic snow and ice major volcanic eruptions are able to spread large amounts of sulfuric acid all over the world acid layers of volcanic origin were detected for the first time a few years ago by hammer in greenland ice the present paper deals with volcanic deposits in the antarctic the different methods that can be used to find volcanic acid deposits in snow and ice cores are compared electrical conductivity sulfate and acidity measurements numerous snow and ice samples collected at several antarctic locations were analyzed the results reveal that the two major volcanic events recorded by h2so4 fallout in antarctic ice over the last century are the eruptions of krakatoa 1883 and agung 1963 both located at equatorial latitudes in the southern hemisphere the volcanic signals are found to be particularly well defined at central antarctic locations apparently in relation to the low snow accumulation rates in these areas it is demonstrated that volcanic sulfuric acid in snow is not even partially neutralized by ammonia the possible influence of antarctic volcanic activity on snow chemistry is also discussed using the three recent eruptions of the deception island volcano as examples only one of them seems to have had a significant effect on the chemistry of snow at a location 200 km from this volcano it is concluded that antarctic volcanic ice records are less complicated than greenland records because of the limited number of volcanos in the southern hemisphere and the apparently higher signal to background ratio for acidity in antarctica than in greenland

a 340 year record of biogenic sulphur from the weddell sea area antarctica detailed records of methanesulphonic acid msa and non sea salt sulpha te nss so have been obtained from ice cores drilled on dolleman island on the east coast of the antarctic peninsula i0 35 2 s 60 55 5 w annual average concentrations of msa arc presented for the period i 652 1992 over this lime span the mean ann ual concen tration of msa is 0 69 eq 1 1 cr 0 33 n 340 the range is 0 13 2 35 eq 1 1 a nd the msa nss s04 2 ratio is 0 22 the high msa concentration reflects the proximity of the weddell sea believed to be a region of high marine phyt0plankton production t he overa ll mean nss so concentration is about 66 of the total sulphate d eposited in the snowfall low frequency variations of msa and oxygen isolope signals correla te closely indicat ing that they may be modulated by similar atmospheric processes positive correlations are observed between the oxygenisotope signature and both l 1sa r 0 4 1 and nss s04 2 r 0 50 signilicant at the 99 level a small negative correlation can be seen between both species and the annual duration or sea ice a t scoria bay laurie island in the south orkneys since 1902 msa r 0 23 and nss so r 0 29 significant at 95 confidence no significant link between high msa concentrations and el nino even ts is observed at this location

climate of the last 500 years high resolution ice core records precipitation accumulating on the earth s ice sheets and ice caps records a variety of physical and chemical information about the atmosphere and in some cases provides unique insight to both the history and the mechanics of the earth s environmental system high resolution well dated dust records from both polar ice sheets suggest a linkage between increased atmospheric dust and cooler temperatures over antarctica but a similar relationship is not observed in ice cores from either greenland or china net accumulation histories for the last 490 years reveal no discemible global pattern although interesting regional differences and similarities exist excess non sea salt sulfate profiles provide

an inter hemispheric volcanic time marker in ice cores from greenland and antarctica a strong volcanic acid signal is clearly registered using an acidity measuring technique in the a d 1259 ice layer in four different greenland ice cores camp century milcent crete and dye 3 this signal is similar in amplitude to the laki iceland a d 1783 volcanic event as recorded in the central and south greenland ice cores measurement of ice layers from corresponding age levels in antarctic ice cores byrd station south pole and j 9 on the ross ice shelf provides similar strong acid signals there is no historical record of a significant volcanic eruption for the period around a d 1260 in the northern hemisphere subsequent chemical analyses of all a d 1259 ice layers show similar compositions we suggest that the a d 1259 signals registered in both greenland and antarctica were caused by the same volcanic disturbance and that its epicenter was located at the earth s equatorial zone which enabled global distribution of the acid gases these results indicate that inter hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone

reassessment of crete greenland ice core acidity volcanism link to climate change previous comparisons of the crete greenland ice core acidity record with climate variations of the last 1 400 years suggested that changes in volcanism may have significantly influenced climate on this time scale however the ice core acidity record consists of volcanically induced spikes superimposed on a background acidity of nonvolcanic origin that varied significantly in amplitude herein the authors produce a record of crete volcanism based solely on an objective definition of individual volcanic events in the ice core record there are 92 acidity peaks in the 1 420 year record since at least 26 of the post 1 600 eruptions are of local icelandic origin they estimate a mean recurrence interval of 20 8 years for hemispheric scale eruptions rich in sulphate on decadal time scales volcanism has varied by a factor of three four over the last 1 400 years however the climate volcanism correlation is considerably less impressive r minus 0 23 than previously concluded r minus 0 52 the good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant little ice age increase the background increase may reflect changes in ocean productivity 24 refs 5 figs 1 tab

active extension in val d agri area southern apennines italy implications for the geometry of the seismogenic belt summary integration of geologic geomorphologic and seismologic data sets is used to reconstruct the recent tectonic evolution and active deformation pattern in the val d agri area located in the seismically active axial sector of the southern apennines italy the western portion of the apennines thrust belt has been affected by pliocene quaternary extension during easterly roll back and crustal delamination of the adriatic slab the bulk of quaternary extension has been accommodated by sw dipping oblique and normal faults which have attained mature morphologic and structural features and nowadays separate mountain ranges from intermontane basins however in the present seismogenic belt coseismic faulting locally occurs on ne dipping structures which might cut the inherited pleistocene landscape in the val d agri basin in spite of the large early middle pleistocene displacement occurred on sw dipping faults bordering its eastern flank our investigations show that the recent basin evolution has been controlled by a ne dipping fault system monti della maddalena fault system mmfs this fault system cuts across the monti della maddalena range west of the agri valley and has not yet created an evident tectonic landscape notwithstanding fault motion since the middle pleistocene might explain geomorphologic and hydrographic anomalies of the agri river and its valley where fault controlled subsidence has captured the river course and produced an aggrading plain within a regional uplift context recent and ongoing motion is documented by fault scarplets in loose deposits 14c ages of palaeosols and the spatial relation with low to moderate instrumental seismicity results from fault kinematic analysis are compatible with fault plane solutions of local and regional seismic events and indicate ne sw oriented extension recognition of the mmfs as a potential seismogenic fault increases the longitudinal extent of the ne dipping morphologically immature seismic sources in the southern apennines and argues against the range bounding fault model for active extension in the region the regional size of the ne dipping seismogenic belt may result from impingement of a mantle wedge beneath the apenninic chain and possibly track the external front of crustal delamination