sub surface structure of la soufriere of guadeloupe lava dome deduced from a ground based magnetic survey abstract in this study we present the analysis and interpretation of a new ground magnetic survey acquired at the soufriere volcano on guadeloupe island observed short wavelength magnetic anomalies are compared to those predicted assuming a constant magnetization within the sub surface the good correlation between modeled and observed data over the summit of the dome indicates that the shallow sub surface displays relatively constant and high magnetization intensity in contrast the poor correlation at the base of the dome suggests that the underlying material is non to weakly magnetic consistent with what is expected for a talus comprised of randomly oriented and highly altered and weathered boulders the new survey also reveals a dipole anomaly that is not accounted for by a constant magnetization in the sub surface and suggests the existence of material with decreased magnetization beneath the soufriere lava dome we construct simple models to constrain its dimensions and propose that this body corresponds to hydrothermally altered material within and below the dome the very large inferred volume for such material may have implications on the stability of the dome

diffuse emission of co2 from showa shinzan hokkaido japan a sign of volcanic dome degassing two soil co2 efflux surveys were carried out in september 1999 and june 2002 to study the spatial distribution of diffuse co2 degassing and estimate the total co2 output from showa shinzan volcanic dome japan seventy six and 81 measurements of co2 efflux were performed in 1999 and 2002 respectively covering most of showa shinzan volcano soil co2 efflux data showed a wide range of values up to 552 g m 2 d 1 carbon isotope signatures of the soil co2 ranged from 0 9 to 30 9 suggesting a mixing between different carbon reservoirs most of the study area showed co2 efflux background values during the 1999 and 2002 surveys b 8 2 and 4 4 g m 2 d 1 respectively the spatial distribution of co2 efflux anomalies for both surveys showed a good correlation with the soil temperature indicating a similar origin for the extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of showa shinzan the total diffuse co2 output of showa shinzan was estimated to be about 14 0 15 6 t d 1 of co2 for an area of 0 53 km2

integrated processing of muon radiography and gravity anomaly data toward the realization of high resolution 3 d density structural analysis of volcanoes case study of showa shinzan lava dome usu japan we have developed an integrated processing method for muon radiography and gravity anomaly data for determining the 3 d density structures of volcanoes with a higher spatial resolution than is possible by conventional gravity inversion in the present paper we demonstrate the performance of the proposed method by performing numerical tests using synthesized data and we present the results obtained by applying the proposed method to a volcano showa shinzan lava dome hokkaido japan we obtained the detailed shape of a vent beneath the dome and detected the presence of solidified dense lava near the top of the dome the results demonstrate the advantage of a hybrid measurement based on both gravity and muon radiography for imaging small structures with sizes of a few hundreds of meters near the surface of a volcano

impact of chi chi earthquake on the occurrence of landslides and debris flows example from the chenyulan river watershed nantou taiwan abstract the chenyulan river watershed in central taiwan was chosen for evaluating the impact of the chi chi earthquake on the occurrence of landslides and for exploring the initial conditions triggering debris flows interpretations of aerial photographs and spot images as well as field investigations were used to identify landslide and debris flow occurrences precipitation data were then utilized to investigate critical conditions leading to the debris flow comparison of five spot images taken between june 1996 before the july 1996 typhoon herb and september 1999 before the chi chi earthquake shows that the landslide area increased from 7 1 106 to 7 5 106 m2 during that time however by january 2000 after the chi chi earthquake the landslide area almost tripled to 20 8 106 m2 measurement of images taken in march and august 2001 reveals that the landslide area had further expanded to 24 2 106 and 27 5 106 m2 respectively significant differences before and after the earthquake are also noticed in 1 the intensity and amount of precipitation required for triggering debris flow 2 the size of contributing drainage basin in which debris flows occurred and 3 the frequency of debris flows after the chi chi earthquake maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1 3 of the pre earthquake figures prior to the chi chi earthquake most debris flows occurred in gullies with slopes greater than 10 and in drainage basins larger than 0 1 km2 conversely after the earthquake debris flows were observed even in gullies with effective drainage area smaller than 0 03 km2 furthermore before the earthquake the debris flow recurrence time in the study area was greater than 5 years whereas six debris flow events have been observed in the 2 years since the earthquake

volcanomagnetic signals during the recent popocatepetl mexico eruptions and their relation to eruptive activity abstract an interdisciplinary approach correlating magnetic anomalies with composition of the ejecta in each eruption as well as with seismicity was used to study the effect of magmatic activity on the local magnetic record at popocatepetl volcano located 65 km southeast of mexico city eruptions began on december 1994 and have continued with dome growth and ash emissions since then the tlamacas tla geomagnetic total field monitoring station located 5 km away from popocatepetl s crater was installed in december 1997 in order to detect magnetic anomalies induced by this activity spatial correlation and weighted difference methods were applied to detect temporal geomagnetic anomalies using tla s record and the teoloyucan magnetic observatory as a reference station weighted differences were applied to cancel the effects of non vulcanogenic external field variations magnetic anomalies over a 2 year time span were classified into four types correlating them with geochemical seismic and visual monitoring of the volcanic activity magnetic anomalies are believed to be caused by magma injection and gas pressure build up which is sensitive to vent morphology and clearing during eruption although some anomalies appear to be thermally related changes in the stress field are very important most magnetic anomalies are short time signals that reverse to baseline level decreasing anomalies 0 5 to 6 8 nt precede eruptions by 1 8 days the presence of a mafic magmatic component was determined by mineral examination and silica and magnesium analyses on the ejecta from the 1997 1999 eruptions whole rock analyses ranged from dacitic 65 sio 2 to andesitic 57 sio 2 with 2 6 6 mgo the higher mgo lower silica samples contain forsteritic olivine fo90 sio 2 does not increase and mgo does not increase with time suggesting ascent of small magma pulses which are consistent with the magnetic data

formation and widening of a north sea tunnel valley the impact of slope processes on valley morphology abstract over the past two decades seismic data from the hydrocarbon industry have become a popular tool for investigating shallow quaternary formations in the north sea basin revealing multiple buried tunnel valleys and other features of glacial origin in this study we incorporate 3d seismic analysis with 2d high resolution seismic data to describe a tunnel valley system in the southern part of the danish north sea basin we document pervasive slumping as the main driver for valley widening in the southern part of the system the slumping and the lateral distribution of slump scars were seemingly controlled by valley steepness and the shape of the valley profile which is partly controlled by the infill rate the system evolved through multiple erosional and depositional phases in the subglacial environment with continued deposition after deglaciation the study provides further evidence of large scale channelized subglacial drainage under past ice sheets and documents a strong impact of valley slope processes in the shaping of the morphology of the upper slopes and shoulders of tunnel valleys

magma prospecting in usu volcano hokkaido japan using magnetotelluric soundings abstract we carried out magnetotelluric mt soundings across usu volcano hokkaido japan which has been active since 1663 the objective was to image an intrusion expected below the formation of 180m high cryptodomes formed during the 1977 78 eruption a ne sw two dimensional resistivity model has been obtained from the inversion in the frequency range from 0 01 to 10 000 hz the major features of the resistivity section are as follows 1 a 50 m thick surficial resistive 1000 10 000 m layer corresponding to the lava layer 2 a relatively conductive 10 1000 m layer from the surface to 200 m depth corresponding to quaternary sedimentary and volcanic rocks 3 beneath the quaternary formations a thick 2 4 km conductive 1 500 m layer of altered tertiary volcanics distributed widely in the volcanic edifice 4 a resistive block 500 1 000 m in the tertiary layer from 200 to 400 m in depth beneath the summit crater forming a striking contrast to the rest of the conductive tertiary layer and probably indicating a cooling intrusion at shallow depth 5 pre tertiary formations consisting of a high resistivity 1000 10 000 m layer overlying a conductive layer with the top of the pre tertiary becoming shallow to the northeast and 6 no deep conductive anomalies corresponding to a magma chamber inferred from petrological studies

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

gravity fields and the interpretation of volcanic structures geological discrimination and temporal evolution abstract a review of gravity data reflecting shallow concealed structures on volcanoes demonstrates that valuable information may be derived on the geological development of such structures and on the dynamic evolution of active volcanoes to a first approximation all recorded examples of anomalous gravity fields associated with volcanoes are concentric with and have sources that lie within the volcanic edifice positive anomalies with wavelengths less than 20 km and amplitudes up to ca 30 mgal characterise mainly basaltic volcanoes from various tectonic settings and are caused by a relatively dense intrusive complex magma body which contrasts with its surroundings either because the body is more mafic than average or more likely because near surface previously erupted materials are uncompacted negative anomalies with wavelengths up to 100 km and amplitudes up to ca 60 mgal occur over much larger volcanic calderas many of which have erupted highly silicic pyroclastic ash and pumice uncompacted silicic caldera infill with a possible contribution from low density magma bodies is responsible for the observed anomalies there is some evidence for a continuum of gravity anomaly types that corresponds to the geological evolution of volcanic systems generally from primitive rift or subduction related basaltic andesite to mature high level silicic calderas repeated microgravity observations over active volcanoes enable magma movements variations in magma input and changes in magma density to be monitored closely dynamic modelling of volcanic systems is providing new evidence on the behaviour of concealed magma bodies and could have considerable potential for predicting eruptive events

3d density modeling with gravity and muon radiographic observations in showa shinzan lava dome usu japan we performed three dimensional density modeling of showa shinzan lava dome usu japan by joint inversion of the gravity anomaly and recently obtained muon radiography data our multilayer emulsion muon detector significantly reduces the background noise in our measurements of the muon flux through the dome the high quality muon data enables us to more accurately reconstruct the density structure of the lava dome compared with our own previous work we find that the lava dome consists of a cylindrical column of massive lava with a diameter of 300 m and that there is no evidence of magma intrusion in the shallow part of the plateau located east of the dome

drainage density and relative relief in humid steep mountains with frequent slope failure previous studies in japanese mountains have shown that drainage density d correlates negatively with relief r and the erosion rate e whereas elsewhere both r and e correlate positively with d to investigate the inconsistency this paper compares two types of d r relations for eight mountain river basins in central japan r is computed from a digital elevation model for 1109 morphometric samples of area 0 5 km 0 5 km drainage networks in these cells were first constructed by map criteria applied previously in japan deeply notched v shaped contours with an angle 53 the resulting d correlates negatively with r confirming preceding studies when drainage lines along shallower hollows were added however the calculated d essentially constant these relations arise from active landsliding in high relief terrains which has eroded steep channel banks into gentle ones the decline of channel banks with increasing r is accelerated in terrains underlain by soft rocks because of rapid erosion the constant d for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains because the d r and d e relations for japan reflect a uniquely japanese physiographic setting characterized by frequent landsliding they differ from those relations for other regions where channelization by gullying predominates 1997 by john wiley sons ltd

geological factors for hazardous debris flows in hoser central taiwan by means of an onsite investigation the largest debris flow in taiwan s history is analyzed in this paper a heavy rainfall of 1 748 mm day occurred during typhoon herb in the hoser area at the end of july 1996 aerial photographic assessment and observations of geological and geomorphological features have contributed to our understanding of this massive destruction mechanisms of the hazardous debris flow are explored and discussed data revealed that the rock discontinuities were a major factor in the voluminous loose materials in the debris flows the heavy and rapid rainfall instantly transported massive amounts of debris flow materials into the center and then quickly funneled them to the lower parts of gullies the heavy slurry became an effective cutting device to erode the side walls and move large quantities of the debris materials to the end of the gullies

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean abstract sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences basin area and relief geography temperature runoff geology lithology ice cover and human activities reservoir trapping soil erosion a new model termed bqart in recognition of those factors accounts for these varied influences when applied to a database of 488 rivers the bqart model showed no ensemble over or underprediction had a bias of just 3 across six orders of magnitude in observational values and accounted for 96 of the between river variation in the long term 30 years sediment load or yield of these rivers the geographical range of the 488 rivers covers 63 of the global land surface and is highly representative of global geology climate and socioeconomic conditions based strictly on geological parameters basin area relief lithology ice erosion 65 of the between river sediment load is explained climatic factors precipitation and temperature account for an additi

scale of relief growth in the forearc of the andes of northern chile arica latitude 18 s the stream profiles of rivers of northern chile reveal two graded segments separated by 20 km long knickzones their formation was initiated in the late miocene in response to surface uplift of the western flank of the altiplano this phase of uplift that was coeval with the shift of deformation from the altiplano to the sub andean zone caused relief to grow at the scale of the whole drainage basin above and beneath these knickzones the presence of braided channels and the absence of erosion on adjacent pediplains suggest no substantial modification in the local relief the knickzones however show bedrock channels and fluvial dissection rates have exceeded erosion rates on adjacent pediplains by two orders of magnitudes hence the data imply that the only geomorphic recorders of relief growth are the knickzones that currently transpose the effects of the late miocene phase of surface uplift from the coast to the altiplano

geophysical characteristics of dacite volcanism the 1977 1978 eruption of usu volcano abstract the 1977 1978 eruption of usu volcano is discussed from the geophysical standpoint as a classic example of dacite volcanism the activities of dacitic volcanoes are characterized by persistent earthquake swarms and remarkable crustal deformations due to the high viscosity of the magmas the former include shocks felt near the volcanoes and the latter accompany formation of lava domes or cryptodomes the hypocenters of the earthquakes occurring beneath usu volcano have been located precisely their distribution defines an earthquake free zone which underlies the area of doming within the summit crater this zone is regarded as occupied by viscous magma the domings within the summit crater forming the cryptodomes have amounted to about 160 m in addition to uplift they showed thrusting towards the northeast as a result the northeastern foot of the volcano has contracted by about 150 m the relation between crustal deformation and earthquake occurrence is examined and it is found that the abrupt domings are accompanied by the larger earthquakes m 3 4 3 both the seismic activity and the ground deformation are shown to have a unique and common energy source the energy of activities of usu volcano consists of the explosive type the deformation type and the seismic type the second and the third are in parallel with each other in discharges and both energies are complementary to the explosive energy the explosive energy and the seismic energy have been calculated for an explosion sequence and it is concluded that the deformation energy is about 10 times greater than the seismic energy the discharge rate of the seismic energy and the upheaval rates of the cryptodomes have continued to decrease since the outburst of the eruption except for a small increase at the end of january 1978 eruptions are governed not only by the supply of the energies but also by the depth of the magma which has gradually approached the surface the last eruption occurred in october 1978 however the crustal deformations and the earthquake swarms are still proceeding as of january 1980 albeit at a lower rate of activity

water and sediment discharge from small mountainous rivers taiwan the roles of lithology episodic events and human activities national science council of taiwan nsc96 2628 m 001 028 u s national science foundation and naval oceanographic office

subsurface structure of usu volcano japan as revealed by detailed magnetic survey abstract a detailed magnetic survey based on 1018 stations was conducted in the usu volcanic region hokkaido japan from the study the following results were obtained 1 the main body of usu volcano is composed of strongly magnetized basaltic somma lavas and weakly magnetized crater fill 2 the southern rim of somma volcano is situated about 200 m south of the present topographic rim suggesting the existence of the buried horseshoe shaped caldera which is thought to have been formed several thousand years ago 3 parts of the mt showa shinzan lava dome formed in the 1943 1945 activity are still occupied with lavas of high temperature above the curie temperature of the ferromagnetic minerals 4 the root of the lave dome of mt showa shinzan has almost the same diameter as that of the dome exposed on the earth s surface 5 an intrusive body about 200 m in diameter may exist at shallow depth in the roof mountain of mt showa shinzan

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

cooling rate and thermal structure determined from progressive magnetization of the dacite dome at mount st helens washington our study of a magnetic anomaly associated with the recently active dacite dome at mount st helens suggests that the dome consists of a hot nonmagnetized core surrounded by a cool magnetized carapace and flanking talus the talus does not contribute to the anomaly because its constituent blocks are randomly oriented temporal changes in the magnetic anomaly indicate that the magnetized carapace thickened at an average rate of 0 03 0 01 m d from 1984 to 1986 petrographic and rock magnetic properties of dome samples indicate that the dominant process responsible for these changes is magnetization of extensively oxidized rock at progressively deeper levels within the dome as the rock cools through its blocking temperature rather than subsequent changes in magnetization caused by further oxidation newly extruded material cools rapidly for a short period as heat is conducted outward in response to convective heat loss from its surface the cooling rate gradually declines for several weeks and thereafter the material cools at a relatively constant rate by convective heat loss from its interior along fractures that propagate inward the rate of internal convective heat loss through fractures varies with rainfall snowmelt and large scale fracturing during subsequent eruptive episodes in accordance with a model for solidification of the 1959 lava lake at kilauea iki hawaii we picture the dome s magnetized carapace as being a two phase porous convective zone separated from the nonmagnetized core of the dome by a thin single phase conductive zone as a consequence of the heat balance between the conductive and convective zones the blocking temperature isotherm migrates inward at a relatively constant rate if the dome remains inactive the time scale for its complete magnetization is estimated to be 18 36 years a forecast which can be refined by shallow drilling into the dome and by continuing studies of its growing magnetic anomaly

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

effects of topography lithology rainfall and earthquake on landslide and sediment discharge in mountain catchments of southeastern taiwan abstract from 1996 through 2007 several heavy typhoons and earthquakes precipitated landslide hazards in southeast taiwan in the present study we analyze the impact of topography lithology rainfall and earthquakes on landsliding and sediment transport by quantifying the landslide ratio ratio of landslide area to catchment area and the sediment discharge for the sinwulu and luye upstream catchments of the peinan river the steep topography in these two catchments causes a large proportion of landslide ratios on slopes to exceeding 50 a condition which accelerates the delivery of landslide debris to the downslope channel the landslide ratios of 0 84 2 30 are obviously related to the rock strength and discontinuity density of the terrain but we find the magnitude of landsliding and sediment discharge to vary with the occurrence of earthquakes typhoon induced rainstorms generate the bulk of sediment discharge in the study catchments though the landslide debris is transported by the huge amounts of runoff produced by rainstorms a contributing factor is the recent occurrence of severe earthquakes which weakened the geomaterial leading in turn to further increases of fluvial sediment during subsequent typhoons additionally the finding that eventual reduction of unit sediment concentration after high magnitude earthquake events reveals that the downslope transport of landslide debris associated with earthquake activity and subsequent typhoon events precipitates a relatively short term 1 3 year increase of erosion rates in these two study areas in southeastern taiwan