triggered deformation and seismic activity under mammoth mountain in long valley caldera by the 3 november 2002 mw 7 9 denali fault earthquake the 3 november 2002 mw 7 9 denali fault earthquake triggered defor mational offsets and microseismicity under mammoth mountain mm on the rim of long valley caldera california some 3460 km from the earthquake such strain offsets and microseismicity were not recorded at other borehole strain sites along the san andreas fault system in california the long valley offsets were recorded on borehole strainmeters at three sites around the western part of the caldera that includes mammoth mountain a young volcano on the southwestern rim of the caldera the largest recorded strain offsets were 0 1 microstrain at po on the west side of mm 0 05 microstrain at mx to the southeast of mm and 0 025 microstrain at bs to the northeast of mm with negative strain extensional high sample rate strain data show initial triggering of the offsets began at 22 30 utc during the arrival of the first rayleigh waves from the alaskan earthquake with peak to peak dynamic strain amplitudes of about 2 microstrain corresponding to a stress amplitude of about 0 06 mpa the strain offsets grew to their final values in the next 10 min the associated triggered seismicity occurred beneath the south flank of mm and also began at 22 30 utc and died away over the next 15 min this relatively weak seismicity burst included some 60 small events with magnitude all less than m 1 while poorly constrained these strain observations are consistent with triggered slip and intrusive opening on a north striking normal fault centered at a depth of 8 km with a moment of 10 16 n m or the equivalent of a m 4 3 earthquake the cumulative seismic moment for the associated seismicity burst was more than three orders of magnitude smaller these observations and this model resemble those for the triggered deformation and slip that occurred beneath the north side of mm following the 16 october 1999 m 7 1 hector mine california earthquake however in this case we see little post event slip decay reflected in the strain data after the rayleigh wave arrivals from the denali fault earthquake and onset of triggered seismicity did not lag the triggered defor mation by 20 min these observations are also distinctly different from the more widespread and energetic seismicity and deformation triggered by the 1992 m 7 3 landers earthquake in the long valley caldera thus each of the three instances of remotely triggered unrest in long valley caldera recorded to date differ in each case however the deformation moment inferred from the strain meter data was more than an order of magnitude larger than the cumulative moment for the associated triggered seismicity

the morphology and distribution of submerged reefs in the maui nui complex hawaii new insights into their evolution since the early pleistocene reef drowning and backstepping have long been recognised as reef responses to sea level rise on subsiding margins during the late pleistocene 500 14 ka hawaiian reefs grew in response to rapid subsidence and 120 m 100 kyr sea level cycles with recent work on the submerged drowned reefs around the big island of hawaii and in other locations from the last deglacial providing insight into reef development under these conditions in contrast reefs of the early pleistocene 1 8 0 8 ma remain largely unexplored despite developing in response to significantly different 60 70 m 41 kyr sea level cycles the maui nui complex mnc forming the islands of maui molokai lanai and kahoolawe provides a natural laboratory to study reef evolution throughout this time period as recent data indicate the reefs grew from 1 1 to 0 5 ma we use new high resolution bathymetric and backscatter data as well as sub bottom profiling seismic data and field observations from rov and submersible dives to make a detailed analysis of reef morphology and structure around the mnc we focus specifically on the south central region of the complex that provides the best reef exposure and find that the morphology of the reefs varies both regionally and temporally within this region barrier and pinnacle features dominate the steeper margins in the north of the study area whilst broad backstepping of the reefs is observed in the south within the au au channel in the central region between the islands closely spaced reef and karst morphology indicates repeated subaerial exposure we propose that this variation in the morphology and structure of the reefs within the mnc has been controlled by three main factors the subsidence rate of the complex the amplitude and period of eustatic sea level cycles and the slope and continuity of the basement substrate we provide a model of reef development within the mnc over the last 1 2 ma highlighting the effect that the interaction of these factors had on reef morphology

pollution assessment of arsenic and other selected elements in the groundwater and soil of the gulf of aqaba saudi arabia forty six soil and groundwater samples were collected from the agricultural farms of the gulf of aqaba coast additionally 24 granitic and marine sedimentary rock samples were collected from the study area the collected samples were analyzed for as al au b ba be fe sb se sn ti and v using inductively coupled plasma mass spectrometry levels of the studied metals in the groundwater samples lie within the acceptable limits of the world health organization who the rock samples exhibit a significant variation in mean metal content from one rock type to another concentrations of as and b in the soil samples were determined to be higher than those of canadian soil quality guidelines csqg and were primarily due to agricultural and seawater inputs chemical weathering of various rock units also plays a significant role the calculations of geoaccumulation index are found to be more reliable than of those of enrichment factor for arsenic contamination levels assessment the study area is not significantly affected by as contamination the correlation coefficient analysis results for the soil and groundwater data reveal a variable degree of correlations between as and other metals in the study area

drowned coralline algal dominated deposits off lanai hawaii carbonate accretion and vertical tectonics over the last 30 ka we present detailed bathymetry remotely operated vehicle rov and submersible observations and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at 150 m t1 and 230 m t2 off lanai hawaii the tops of the terraces are veneered by relatively thin b5 m in situ accumulations of coralline algal nodule coralgal nodule halimeda and a derived oolitic facies deposited in intermediate 30 60 m to deep fore reef slope settings 60 120 m the data are used to develop a sedimentary facies model that is consistent with eustatic sea level variations over the last 30 ka both nodule facies on t1 and t2 initiated growth 30 29 ka following a fall in sea level of 50 m and increase in bottom currents during the transition from marine isotope stage 3 to 2 the nodules accreted slowly throughout the last glacial maximum when sea level was relatively stable drowning occurred during the early deglaciation 17 16 ka and was marked by the complete drowning of coralline algal nodules facies on t2 and incipient drowning of coralgal facies on t1 abrupt sea level rise during the middle deglaciation perhaps associated with global meltwater pulse 1a 14 15 ka finally drowned the coralgal facies on t1 which in turn was overlain by a deep water halimeda facies or an oolitic facies derived from upslope our data indicates that lanai has experienced relatively little vertical tectonic movement over the last 30 ka using paleobathymetric data derived from the sedimentary facies age vs depth relationships and published sea level curves we estimate that lanai could be either slowly uplifting or subsiding but at rates b0 1 m kyr uplift or b0 4 m kyr subsidence over this 30 kyr period d 2005 elsevier b v all rights reserved

age of tilted reefs hawaii submerged carbonate reefs are preserved as a series of submarine terraces between molokai and hawaii along a 200 km span of the southeastern hawaiian ridge limestones from two of the terraces have been sampled from submersibles and dated radiometrically at 13 and 120 ka recognition that the terraces are tilted permits assignment of about a dozen terraces from 150 to 1300 m depth to eight general reef platforms these reefs were drowned by the combined effects of island subsidence and sea level rise at the end of successive glacial stages from 13 to 647 ka the platforms are tilted 5 m km southeast toward the locus of volcanic loading centered on the island of hawaii the end of the active period of volcanic shield building is represented on each nonactive volcano by a submerged change in slope dating of this slope change by reference to the dated reefs provides independent evidence that shield building ended at about the same time that the volcano changed from eruption of tholeiitic to alkalic basalt the variation in depth of the dated tilted reefs along the ridge indicates that the end of subsidence follows the end of shield building by about one half million years the present northwest margin of major subsidence probably crosses southeast maui during the last half million years the rate of southeast migration of the beginning of both subsidence and of tholeiitic volcanism does not appear to have increased however the rate of southeast migration of the end of both subsidence and of tholeiitic volcanism has apparently increased this shortening of the life history of the younger volcanoes implies an increase in eruption rates

subsidence of puna hawaii inferred from sulfur content of drilled lava flows abstract sulfur was analyzed in more than 200 lava samples from five drill holes located on the east rift zone of kilauea volcano on the island of hawaii the sulfur content is a gage of whether lava was erupted subaerially low sulfur or erupted subaqueously high sulfur despite considerable variation sulfur is generally low less than 0 025 in the upper part of the holes begins to increase at a depth of 250 320 m below sea level and generally reaches a high level greater than 0 1 indicative of steady submarine eruption at 330 450 m below sea level assuming that the island is subsiding at 2 4 mm yr an analysis of these data indicates that part of the variation in sulfur concentration results from past eustatic oscillation of sea level and that the volcano at the drill hole site finally emerged for the last time about 98 ka the long term average rate of lava accumulation is roughly 4 4 mm yr and upward growth of the volcano at the drill hole area is about 2 mm yr in excess of subsidence

geomorphometry and processes that built necker ridge central north pacific ocean abstract necker ridge is an enigmatic 650 km long narrow linear aseismic bathymetric feature that rises 2500 to 3000 m above the abyssal seafloor south of the hawaiian ridge the ridge is the largest of a series of aseismic ridges that emanate from the eastern side of the mid pacific mountains outward towards the northeast the trend of necker ridge is at an angle to fracture zones and spreading centers in the region so its origin is controversial yet it is a major feature on this part of the cretaceous pacific plate the entire feature from necker island on the hawaiian ridge to the eastern mid pacific mountains including the adjacent abyssal seafloor was mapped in 2009 and 2011 with the latest generation of multibeam echosounders the detailed bathymetry shows the ridge to be constructed of a series of stacked thick 200 400 m volcanic flows that can be traced along the trend of necker ridge for 100 s of km this continuity suggests that the volcanism erupted simultaneously along almost the entire length of the feature and not as spatially episodic areas of extrusion three relatively flat platforms occur on the summit region presumably constructed of shallow water carbonates when these portions of the ridge were at sea level a conspicuous lack of thick pelagic sediment on the non platform ridge summit and flanks is seen throughout the ridge the lack of landslides along the length of the ridge is equally puzzling the southern end of the ridge is connected by a saddle to the mid pacific mountains whereas the northern end of the ridge is buried by an archipelagic apron of the southern flank of the hawaiian ridge

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

geochemical assessment of groundwater contamination with special emphasizes on fluoride a case study from midyan basin northwestern saudi arabia water samples for chemical analyses were collected in january 2012 a total of 72 samples of groundwater were collected from 72 boreholes in the midyan basin northwestern saudi arabia samples were collected in polyethylene bottles and preserved and the used analytical techniques were in accordance with the standard methods from american public health association geochemical analyses of the groundwater samples from midyan basin reveal the concentration of fluoride f between 0 98 and 2 1 mg l other parameters e g ph ec tds hco3 so4 no3 cl k na mg and ca have been found in a variable proportion among them the concentration of ec hco3 k na and mg is higher than the permissible limits according to thermodynamical considerations most of the analysed samples are graded under saturated with respect to calcite and fluoride while saturation has been observed in some samples the under saturation could probably be attributed to low concentration of calcite and fluoride in the studied wells fluoride concentration shows weak positive correlation with ec tds na cl and so4 factors controlling the concentration of fluoride f in the studied samples are the area climate water chemistry and the presence of accessory minerals in the rocks through which groundwater is circulating besides the anthropogenic activities in the area

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

heavy metal concentrations in surface sediments from the two coastal inlets golden horn estuary and izmit bay of the northeastern sea of marmara a total of 57 surficial sediment samples collected in the golden horn estuary and izmit bay northeastern marmara sea was analyzed for the heavy metals fe mn cr ni co zn pb and cu and the results were compared with various natural and anthropogenic sources it was observed that the concentrations of zn cu pb and to some extent cr in the golden horn sediments are comparable with those in most other seas in the vicinity of highly industrialized and densely populated regions based on calculations from the metal al and metal fe ratios the bottom sediments of golden horn were found to be enriched in zn cu pb and to a lesser extent cr by factors of up to 192 compared with the regional background levels of these metals fe mn co and to some extent ni are mostly at natural levels in contrast the metal levels of the bottom sediments in izmit bay are significantly lower and they appear to be controlled by lithogenic rather than the anthropogenic influences highly significant correlation coefficients between the metals zn cu and pb are widely attributed to the common sources of these metals the metal smelters and shipyards in the vicinity of the areas studied based on the numerical value of the geoaccumulation index of heavy metals it was found that the bottom sediments of izmit bay can be regarded as basically uncontaminated exceptionally high igeo values are found for the bottom sediments of the golden horn indicating moderate to extreme contamination in this region by the metals pb zn cu and cr the presence of a large number of anthropogenic metal point sources higher river run off via the two major creeks particularly coastal topography and hydrodynamic conditions associated with the very high sedimentation rates all strongly favour the accumulation of anomalously high metal concentrations in the golden horn estuary while the opposite is true for izmit bay

dominant influence of volcanic loading on vertical motions of the hawaiian islands abstract rates of island vertical motion above intra plate hotspots record the processes that arise from interactions between lithospheric plates and mantle plumes to assess the contribution of mantle and lithospheric processes to surface motion above the hawaiian hotspot we compare simple models of lithospheric deformation to vertical motion rates measured from dated paleoshorelines and tide gauge records in the hawaiian islands our analysis shows that observed uplift and subsidence rates mainly record the flexural response of the lithosphere to volcanic loads the effective elastic plate thickness that best fits the spatial distribution of subsidence and uplift rates is 40 km consistent with previous estimates based on total vertical deflection because volcanic loading dominates the vertical motion signal hawaiian islands appear to follow a predictable trajectory of vertical motion when they reside within one flexural half wavelength of the active volcanic center islands initially subside at rapid and decreasing rates in the first 1 myr following their construction uplift relatively slowly 1 2 5 myr following their construction and eventually subside again but at slow rates within 5 myr of their construction this observed pattern of uplift and subsidence is consistent with the pattern of vertical motion predicted to result from volcanic loading at the hawaiian hotspot lithospheric migration over the long wavelength topographic swell associated with the hawaiian hotspot has a comparatively minor influence on island uplift and subsidence its contribution to island vertical motion is not readily observed in our data with the possible exception of some uplift observed in the past 500 kyr on o ahu that might correspond to non steady state behavior of the hawaiian plume

distribution of arsenic iii arsenic v and total inorganic arsenic in porewaters from a thick till and clay rich aquitard sequence saskatchewan canada abstract inorganic arsenic species were measured in the porewaters collected from eighteen piezometers installed between 3 and 91 4 m below ground in a thick till and clay rich aquitard sequence located in southern saskatchewan to investigate the distribution of and controls on arsenic speciation in the sequence aqueous concentrations of as v as iii and total as are in the range of 0 31 97 0 71 21 and 3 2 98 ppb respectively profiles of as iii and as v concentration distribution with depth broadly track that of total as erratic increases to 15 2 m then more uniform concentrations to 88 m aqueous arsenic is accumulated at the upper redox transition zone 6 14 m the alkaline porewater at 91 4 m contains the highest concentrations of as v and total as which might result from the facilitated desorption of arsenate from the host solid due to decrease of positive surface charge of the oxides in alkaline solution the ratio of as v as iii is greater than unity in the uppermost oxidized porewater 3 m less than unity from 4 6 to 71 6 m and greater than unity in the lowest four porewaters 76 2 to 91 4 m in the 3 m porewater low as iii but high as v as iii is due to the oxidized nature of the near surface weathered till the high as v as iii in the deepest porewater at 91 4 m likely results from the enhanced and heterogeneous oxidation of as iii to as v on clay mineral surfaces in the alkaline solution total as and arsenic speciation may not be controlled by as fe or mn concentrations in the host till or clay dissolved as v and total as positively covary with aqueous chloride whereas dissolved as iii is independent of aqueous chloride aqueous as iii and to a less extent as v and total as are positively correlated with dissolved mn in the till in the clay aqueous as v and total as show strong negative covariation with mn however aqueous as iii as v and total as exhibit almost no correlation with total dissolved fe in the till the as v as iii ratio has strong negative correlation with dissolved mn but positive covaration with dissolved chloride generally good agreement between the redox potentials eh calculated from aqueous as v and as iii concentrations and those measured by a pt electrode throughout most of the unoxidized till suggests the suitability of using as v as iii redox couple as a redox indicator for the studied aquitard system however large negative bias of the calculated eh from the measured eh in the oxidized till upper unoxidized till and the clay is attributed to errors associated with the field measurements of eh

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

posterosional volcanism in the cretaceous part of the hawaiian hotspot trail multibeam bathymetry and seismic reflection profiling shows the cretaceous products of the hawaiian hotspot to be a ridge of coalesced guyots that prolong the n nw trend of the more isolated paleocene emperor seamounts a 10 000 km2 plateau detroit plateau where the trail changes strike to nw and the obruchev rise hotspot ridge which extends to the kamchatka trench the northernmost guyots were submerged and tilted southeast by the load of new shield volcanoes added to the end of the chain then secondary volcanism built small cones on their summit platforms and in a gap between two guyots dredged rock samples and the distribution of the cones indicates that on one guyot these submarine eruptions were in the alkalic postshield stage of hawaiian volcanism and at another were probably in the alkalic rejuvenated stage seamount building eruptions at detroit plateau produced lavas nepheline melilitites that belong geochemically to the alkalic rejuvenated stage and are very similar to pleistocene lavas in the hawaiian islands however these eruptions postdated passage off the hotspot plume by a much longer time than the 0 5 2 5 m y observed in the hawaiian islands and were probably initiated by different tectonic processes

subsidence and volcanism of the haleakala ridge hawaii abstract side looking sonar gloria mapping has revealed a series of four arcuate bands of high sonic backscatter on the crest of the haleakala ridge a major rift zone ridge extending 135 km east of the island of maui dredge recovery indicates that the shallowest of these bands is a drowned coral reef and the deeper bands are also inferred to be coral reefs the reefs occur above a prominent submarine bench 1500 2500 m deep on the ridge h terrace that marks the shoreline at the end of vigorous shield building of haleakala volcano when lava flows ceased crossing and reworking the shoreline since their growth these reefs have subsided as much as 2200 m and have tilted systematically about 20 m km southward as a result of post reef volcanic loading on the island of hawaii whose center of mass is about directly south of the haleakala ridge the 234u 238u age of the dredged coral is 750 13 ka in reasonable agreement with an age of 850 ka for the underlying h terrace previously estimated from its relationship to other dated reefs to the southwest basalt glass fragments dredged from the haleakala ridge below the h terrace are tholeiitic and contain high sulfur indicative of eruption in water deeper than 200 m basalt glass fragments associated with the reefs above the h terrace are dominantly tholeiitic and contain intermediate sulfur contents indicative of subaqueous eruption in shallow near shore conditions one alkalic glass fragment was recovered above the h terrace these relations indicate that the morphologic end of shield building as recorded by construction of the h terrace was not accompanyed by a change from tholeiitic to alkalic basalt instead tholeiite eruptions continued for some time before the erupted lava became alkalic

coastal lava flows from mauna loa and hualalai volcanoes kona hawaii a major carbonate reef which drowned 13 ka is now submerged 150 m below sea level on the west coast of the island of hawaii a 25 km span of this reef was investigated using the submersiblemakali i the reef occurs on the flanks of two active volcanoes mauna loa and hualalai and the lavas from both volcanoes both underlie and overlie the submerged reef most of the basaltic lava flows that crossed the reef did so when the water was much shallower and when they had to flow a shorter distance from shoreline to reef face lava flows on top of the reef have protected it from erosion and solution and now occur at seaward projecting salients on the reef face these relations suggest that the reef has retreated shoreward as much as 50 m since it formed a 7 km wide shadow zone occurs where no hualalai lava flows cross the reef south of kailua these lava flows were probably diverted around a large summit cone complex a similar shadow zone on the flank of mauna loa volcano in the kealakekua bay region is downslope from the present mauna loa caldera which ponds mauna loa lava and prevents it from reaching the coastline south of the mauna loa shadow zone the 150 m reef has been totally covered and obscured by mauna loa lava the boundary between hualalai and mauna loa lava on land occurs over a 6 km wide zone whereas flows crossing the 150 m reef show a sharper boundary offshore from the north side of the subaerial transition zone this indicates that since the formation of the reef hualalai lava has migrated south mantling mauna loa lava more recently mauna loa lava is again encroaching north on hualalai lava

geochronology of drowned hawaiian coral reefs abstract two deeply submerged coral reefs were sampled with the hurl submersible pisces v off the islands of hawaii and maui an ancient fringing reef at 950 m depth on the kohala slope of hawaii was observed from deep towed camera photographs and during submersible operations a second reef at 1650 m depth on the haleakala slope of maui was observed on side scan images deep towed camera photographs and during submersible observations ages of the two reefs were determined by electron spin resonance dating with a signal intensity for aragonitic coral at g 2 0007 used to ascertain the accumulated dose by the additive dose method uranium concentration was measured by neutron activation analysis the chronology of the reefs indicates that drowning coincided with periods of rapid global climate change at the termination of continental glaciation at approximately 250 ka and 340 ka the drowning events correlate with oxygen isotope stage boundaries 7 8 and 9 10 these data support models of reef drowning on subsiding volcanic edifices

modeling the influence of rainfall gradients on discharge bedrock erodibility and river profile evolution with application to the big island hawai i motivated by convex concave bedrock river profiles developed across a climate gradient on the wetside of the kohala peninsula of the big island of hawai i we numerically model how rainfall gradients may influence longitudinal fluvial incision patterns first we model transient profile adjustment with two tectonic boundary conditions subsidence and uplift in this generalized analysis we assume that rainfall gradients only influence incision by modifying the relation between upstream drainage area and local discharge using a detachment limited model downstream increases in rainfall lead to profile convexities during transient adjustment in both tectonic settings and this is the opposite of the predicted increase in profile concavity that would develop in a steady state uplifting profile a transport limited erosion model develops only concave channel profiles without clear signatures of the rainfall pattern second we model the development of convex concave transient profiles and incision patterns on kohala using a detachment limited model if rainfall gradients only influence incision through the local discharge reasonable rainfall gradients can only develop channel convexities that are much smaller than those observed instead we hypothesize that local bedrock erodibility increases with the degree of rainfall dependent chemical weathering when local erodibility is assumed to scale with local rainfall rate the model can produce convex concave profiles similar to those observed in kohala our results suggest that changes in local bedrock erodibility due to local climate dependent weathering may be an important mechanism by which climate influences landscape form and rates of evolution this hypothesis requires further testing in this study area and beyond