Frontal Ridge Research Articles

Role of gas hydrates in slope failure on frontal ridge of northern Cascadia margin

Several slope failures are observed near the deformation front on the frontal ridges of the northern Cascadia accretionary margin off Vancouver Island. The cause for these events is not clear, although several lines of evidence indicate a possible connection between the occurrence of gas hydrate and submarine landslide features. The presence of gas hydrate is indicated by a prominent bottom-simulating reflector (BSR), at a depth of ∼265–275 m beneath the seafloor (mbsf), as interpreted from vertical-incidence and wide-angle seismic data beneath the ridge crests of the frontal ridges. For one slide, informally called Slipstream Slide, the velocity structure inferred from tomography analyses shows anomalous high velocities values of about 2.0 km s−1 at shallow depths of 100 mbsf. The estimated depth of the glide plane (100 ± 10 m) closely matches the depth of these shallow high velocities. In contrast, at a frontal ridge slide just to the northwest (informally called Orca Slide), the glide plane occurs at the same depth as the current BSR. Our new results indicate that the glide plane of the Slipstream slope failure is associated with the contrast between sediments strengthened by gas hydrate and overlying sediments where little or no hydrate is present. In contrast, the glide plane of Orca Slide is between sediment strengthened by hydrate underlain by sediments beneath the gas hydrate stability zone, possibly containing free gas. Additionally, a set of margin perpendicular normal faults are imaged from seafloor down to BSR depth at both frontal ridges. As inferred from the multibeam bathymetry, the estimated volume of the material lost during the slope failure at Slipstream Slide is about 0.33 km3, and ∼0.24 km3 of this volume is present as debris material on the ocean basin floor. The 20 per cent difference is likely due to more widely distributed fine sediments not easily detectable as bathymetric anomalies. These volume estimates on the Cascadia margin are approaching the mass failure volume for other slides that have generated large tsunamis—for example 1–3 km3 for a 1998 Papua New Guinea slide.

Synopsis of Paxillus MacLeay, 1819 (Coleoptera: Passalidae): distributional records and descriptions of four new species from Brazil.

Paxillus MacLeay, 1819 (Coleoptera: Passalidae) is redescribed, with new distributional records and descriptions of four species from Brazil. Paxillus reyesi new species is characterized by the first antennomere of antennal club reduced, slightly longer than half of the second antennomere; mesosternal scar straight, wide and deep. Paxillus chapadensis new species from the Chapada dos Guimarães (Mato Grosso, Brazil) has prostenal process centrally impressed with an opaque depression; and the scape of the antenna with a subapical dorsal spine, shallow ventral depression, and few erect setae. Paxillus manausensis new species from Manaus (Amazonas, Brazil) has high frontal ridges; mid-frontal tubercles high, acuminate and larger than the internal tubercles; and the central tubercle short. Paxillus uaupesensis new species from Uaupes (Amazonas, Brazil) has the mesosternal scar opaque, elongate and depressed; and the scutellum depressed. Diagnostic redescriptions and illustrations of known species from Brazil, a key to all known species, and a checklist with distributional data are provided.

Review of Teiid Morphology with a Revised Taxonomy and Phylogeny of the Teiidae (Lepidosauria: Squamata)

Despite advances within particular groups, systematics of the Teiidae has long been unsatisfactory, because fewmorphological characters have been described for this family. Consequently, most species have been assigned to the large,polyphyletic, and poorly defined genera Ameiva and Cnemidophorus. We describe 137 morphological characters andscore them for most species of Neotropical Teiidae. Important, but previously undescribed, character suites include pupilshape; the frontal ridge; longitudinal division of the interparietal; the rostral groove; patterns of supraciliary fusion; thepreauricular skin fold; the “toothy” first supralabial; modified apical granules; the pectoral sulcus; expansion of scales atthe heel; tibiotarsal shields; scales between the digital lamellae along the postaxial edges of the toes; scale surfacemicrostructure of macrohoneycomb, macroridges, or lamellae; distribution patterns and morphology of lenticular scaleorgans; types of epidermal generation glands; and several hemipenial structures. We propose a new taxonomy of theTeiidae based on recovered evolutionary history and numerous morphological characters surveyed in this study. Werecognize three subfamilies: Callopistinae new subfamily, Teiinae Estes et al., and Tupinambinae Estes et al. To resolvepolyphyly of Ameiva and Cnemidophorus, we erect four new genera for various groups of Neotropical Teiidae: Ameivulanew genus, Aurivela new genus, Contomastix new genus, and Medopheos new genus. We resurrect Holcosus Cope fromthe synonymy of Ameiva and Salvator Duméril and Bibron from the synonymy of Tupinambis. On the basis of sharedderived characters, we propose new species groups of our redefined Ameiva and Cnemidophorus. We incorporate our newcharacters into a key to the genera and species groups of Teiidae. A phylogenetic hypothesis of Teiidae based onmorphological characters differs substantially from hypotheses based on mitochondrial DNA. The phylogeny based onmorphology is consistent with well-established biogeographic patterns of Neotropical vertebrates and explains extreme morphological divergence in such genera as Kentropyx and Aurivela.

Schmidt-hammer exposure-age dating (SHD) of rock glaciers in the Schöderkogel-Eisenhut area, Schladminger Tauern Range, Austria

Schmidt-hammer rebound values ( R-values) enable relative-age dating of landforms, with R-values relating to degree of weathering and therefore length of exposure. This method – recently termed as Schmidt-hammer exposure-age dating (SHD) – was applied to date five rock glaciers (size range, 0.01–0.12 km2) and one recent rockfall deposit at the study area Schöderkogel-Eisenhut, in the Schladminger Tauern Range (14°03′E, 47°15′N), Austria. The rock glaciers consist of gneiss or high metamorphic series of mica-schist that are comparable in their R-values. Four of them are relict (permafrost absent) and one is intact (containing patches of permafrost). On each of the five rock glaciers, SHD was carried out at 4–6 sites (50 measurements per site) along a longitudinal transect from the frontal ridge to the root zone. Results at all five rock glaciers are generally consistent with each other sharing statistically significant R-values along transects. The range between the highest and the lowest mean R-value at each of the five rock glaciers is 9.9–5.2. Using rock glacier length and surface velocity data from nearby sites, the rock glacier development must have lasted for several thousand years. Furthermore, by using SHD results from rock glaciers of known age from other sites in the region with comparable geology, approximate surface ages of 6.7–11.4 ka were estimated. This indicates long formation periods for all five rock glaciers. Our results suggest that many of the 1300 relict rock glaciers in central and eastern Austria were formed over a long period during the Lateglacial and Holocene period.

Cenozoic Development of the Lapstone Structural Complex, Sydney Basin, New South Wales

The Lapstone Structural Complex is an association of monoclines and high-angle reverse faults that occupies the frontal ridge of the lower Blue Mountains, west of Sydney. Permian–Triassic movements have been proposed on the basis of unpublished seismic profiles reportedly showing abrupt stratigraphic thickness variations in the Sydney Basin succession across the Lapstone Structural Complex and indicative of syn-depositional deformation. In a companion paper, we present an interpretation of recently reprocessed seismic data and show that the Lapstone Structural Complex played no role during Sydney Basin sedimentation. Paleomagnetic data collected from two monoclines are interpreted to bracket development of the Lapstone Structural Complex within the mid-Cretaceous to Miocene interval. Cenozoic uplift of the frontal ridge of the lower Blue Mountains is shown by uplifted semi-consolidated gravels (Rickabys Creek Gravel). A Paleogene timing of uplift was proposed from modelling of landscape development. Association of structures of the Lapstone Structural Complex with the uplifted lower Blue Mountains is most simply explained by a Paleogene age for these structures. Evidence for additional neotectonic activity along the Lapstone Structural Complex reflects the modern compressive stress regime associated with the transpressional plate boundary in the South Island of New Zealand. A Paleogene age for the uplift of the Blue Mountains is consistent with the high relief of this region in contrast to more stable regions of the highlands of eastern Australia characterised by low local relief, reflecting antiquity.

Frontal ridge slope failure at the northern Cascadia margin: Margin-normal fault and gas hydrate control

On the northern Cascadia accretionary margin off Vancouver Island, Canada, there are numerous sedimentary slide features near the base of the slope, and significant amounts of gas hydrate found beneath the ridge suggest a possible connection. A 2-km-wide collapse structure with a 300-m-high headwall has been studied by multibeam bathymetry and a single-channel seismic reflection grid. Migrated seismic reflection lines on the frontal ridge image multiple 15–75-m-high seafloor scarps perpendicular to the margin that are the seafloor expressions of normal faults that cut deeply into the sediment section. Two of the largest faults are aligned with the sidewalls of the slide, indicating that the lateral extent of the collapse is fault controlled. The presence of marine gas hydrate beneath the ridge is based on a widespread hydrate bottom-simulating reflector (BSR), high velocities determined by ocean bottom seismograph data, and sediment core samples and downhole logs collected by the Integrated Ocean Drilling Program at Site U1326. The depth of the BSR at 255 (±15) m coincides closely with the estimated depth of the glide plane beneath the slide. This suggests that the base of the slope failure is related to the contrast between strong hydrate-cemented sediments above the BSR and underlying weak sediments containing free gas. Strong earthquake shaking on this convergent margin likely provides the trigger for the slide.

Politolana sanchezi sp. nov. (Crustacea: Isopoda: Cirolanidae), a new benthic bioturbating scavenger from bathyal soft-bottoms of the southern Bay of Biscay (northeastern Atlantic Ocean)

A new species of the genus Politolana (Crustacea, Isopoda, Cirolanidae) is described, based on specimens collected from the Le Danois Bank (‘El Cachucho’ fishing ground), southern Bay of Biscay, northeastern Atlantic Ocean. Politolana sanchezi sp. nov. can be distinguished from P. microphthalma (the only Politolana species recorded in boreal European waters) by larger eyes, presence of chromatophores on pereon and pleon, antennae reaching to the middle of the second pereonite, lateral margin of the frontal ridge dividing eyes, superior meral lobe of pereopod 1 reaching midpoint of the propodus, distal end of uropodal endopod subacute and pleotelson apex broadly convex with small medial point. An identification key to the world species of Politolana is presented. The new species has been found living on muddy-fine sandy bottoms of the southern Bay of Biscay and western Galicia, between 480 and 791 m depth. According to the present findings, it belongs to the benthic scavenger guild recognized on continental slopes. Its scavenging and bioturbating behaviour at the sediment-water interface are described from in situ trophic experiments with a fish-baited trap combined with a time-lapse recording camera.

Tectonic constraints on watershed development on frontal ridges: Mohand Ridge, NW Himalaya, India

Uplifting frontal ridges are one of the most conspicuous geomorphic features that mark the frontal parts of actively converging mountain belts. Growth of these ridges can lead to the simultaneous development of a drainage system that is defined by watersheds, stream network and long profiles of channels. In the present study, shape parameters of watersheds, stream network characteristics and pattern of network growth, shape of long profiles, and the SL index have been investigated in a part of NW Himalaya to understand the relationship between endogenic tectonic processes and exogenic fluvial processes. This explains the tectonic control on drainage systems in the uplifting frontal ridge. This watershed analysis was carried out using a Digital Elevation Model (DEM) and a number of anomalies have been identified and analysed. The most striking is the asymmetric development of watersheds on either side of an almost straight ridge crest. Watershed asymmetry along the ridge crest is characterized by larger area and less elongated watersheds in the southern flank (forelimb) in comparison to the northern flank (backlimb). Drainage network and long profile analysis establishes that the larger watershed area in the forelimb is due to dominance of headward erosion and its impact on drainage network growth. Dominance of headward erosion is due to slope variation in response to forelimb development along a fault-related fold. Even through, headward erosion has shifted the ridge crest; it is parallel with the trace of the Himalayan Frontal Thrust (HFT). The parallel ridge crest with reference to the HFT is indicative of the tectonic control of the HFT on the development of the watersheds. Hence, a well developed linkage between tectonic processes (fold development) and surface processes (headward erosion) is responsible for variation in watershed and drainage network pattern across the ridge crest. The study also investigates the role of planform ridge curvature on watershed development. The effect is more pronounced on an asymmetric ridge, such as the Mohand ridge, than on a symmetric ridge.

A taxonomic study of the genus Austrohancockia Günther (Orthoptera:Tetrigoidea: Tetrigidae)

Eleven species of Austrohancockia Günther were systematically researched in this paper. One species, Austrohancockia tuberfemora sp. nov., is described as new to science. This new species can be distinguished from Austrohancockia guangxiensis Zheng et Jiang, 1998, but differs in vertex and frontal ridge forming a right-angle; midkeel of pronotum interrupted, not conspicuous; pronotum reaching the knee of hind femur; width of fore femora equal to the width of middle femora; lower margins of fore and middle femora with one big teeth; third pulvillus of first segment of hind tarsi longer than first and second, apices of first and second sharp, apices of third obtuse. An updated key to the species of Austrohancockia is presented. The type specimens are deposited in the Institute of Zoology, Shaanxi Normal University, Xi’an, China.

The larvae of the burrowing mayfly genus Tortopus (Ephemeroptera: Polymitarcyidae)

The larval stage of Tortopus is redescribed based on three species: T. puella from North America, the only species of the genus previously known from larva, and the larvae of T. obscuripennis and T. sarae from South America described here. Generic characters of the larva include: relatively large finger-like gill near base of maxilla, inner margin of mandibular tusks with a subdistal tubercle, straight or weakly convex frontal ridge present between antennae, reduced unilamellated gill on abdominal segment I. Additionally the male imagines of both Neotropical species are described for the first time, and T. obscuripennis is recorded from Bolivia. Diagnoses, SEM photographs, and illustrations are given for the new stages described and for the identification of the three Tortopus species known as larvae.

Description of the post larva of star pipefish,halicampus punctatus (syngnathidae, gasterosteiformes) first found in the southwestern east sea, Korea

Larval specimens ofHalicampus punctatus were collected off Ulsan and Uljin in December 2002 (three specimens) and off Ulsan in December 2003 (one specimen). These specimens are characterized by the following morphological characteristics: rings, 14 + 35 = 49; subdorsal rings, 1 + 3 = 4; dorsal fin rays, 19 – 20; pectoral fin rays, 14 – 15; anal fin rays, 9; head length (HL), 5.8 – 6.7 in the standard length; snout length, 1.9 in HL; snout depth, 3.7 – 5.2 in snout length. The number of caudal fin rays 9 is less than those of the other species in the same genus 10. Wide stripe bands composed of small pigments are shown in the trunk and the tail. Melanophores are not found in the dorsal fin, the pectoral fin, and the anal fin except the caudal fin. The supraoccipital crest is on the head. The frontal ridge is on the dorsal side of front trunk. The blanched ridges on the opercular are fused with a main ridge like a tree branch. A few branched ridges that are small and narrow on the trunk and the tail are fused with the main ridges. We report these specimens as the first record in Korea and name them ‘Byeol-silgo-ki’ in Korean.

A new pygmy pipehorse (Pisces: Syngnathidae: Idiotropiscis) from eastern Australia

A new species of pygmy pipehorse, Idiotropiscis lumnitzeri, is described from a female and two male specimens collected in the Sydney region, New South Wales, Australia. It can be distinguished from its congeners, I. australe (Waite & Hale, 1921) and I. larsonae (Dawson, 1984), in having a shorter and more posteriorly positioned frontal ridge dorsally on the head, a very short trunk (slightly longer than head, versus clearly longer than head), and in having a longer snout (2.2-2.6 in head, versus 2.8-3.2 in I. australe and 3.7-3.8 in I. larsonae).

Nasopharyngeal rhabdomyosarcoma in a patient with hypohidrotic ectodermal dysplasia syndrome

Hypohidrotic ectodermal dysplasia (Christ-Siemens-Touraine syndrome) is characterized by partial or complete absence of sweat glands, hypotrichosis, hypodontia, prominent frontal ridges and chin, saddle nose, sunken cheeks, thick, everted lips, large ears and sparse hair. While association of other ectodermal dysplasia syndromes with tumors such a non-Hodgkin's lymphoma, hamartoma, keratoakanthoma, Merkel-cell cancer, squamous-cell carcinoma, syringofibroadenomatosis has been reported, association of hypohidrotic ectodermal dysplasia and a tumor has not been reported. In a five-year-old male patient admitted with nasal obstruction and nasal mass complaints, we have reported firstly an association of hypohidrotic ectodermal dysplasia and nasopharyngeal rhabdomyosarcoma.

A Reevaluation of the Origin of Blocky Landforms in Cirques in the Japanese Alps

In the Japanese Alps, only a few rock glaciers associated with mountain permafrost have been identified, although the present lower limit of mountain permafrost is estimated to lie at 2, 500 to 2, 800m a. s. l. and permafrost is considered to have been distributed more widely during the previous cold periods than at present. The purposes of this paper are to reexamine the origin of blocky landforms in cirques, which have often been interpreted as moraines or protalus ramparts, and to reconstruct rock glacier distribution in the Japanese Alps. As a result of air-photo interpretation and field observations, many rock glaciers were identified in the Northern and Southern Japanese Alps. These landforms comprise transverse low ridges and furrows, a continuous marginal ridge, or a tongue or festoon-shaped frontal ridge located at the foot of talus. At one of these landforms, a two-layer structure, comprising a matrix-supported finer debris layer overlain by an open-work bouldery layer, was observed. These morphological and structural characteristics are similar to those of typical fossil rock glaciers, suggesting that the blocky landforms are fossil rock glaciers rather than moraines or protalus ramparts. Therefore attention should be paid to the origin of blocky landforms when past glacial distribution and the paleoenvironment are reconstructed using landforms.

Measurement and theory of ploughing boulder movement

AbstractAnalysis of the characteristics, distribution and rate of movement of ploughing boulders reveals several attributes that throw light on the mechanism of boulder movement. Ploughing boulders occur only in areas of active solifluction, on frost‐susceptible soils with low plastic and liquid limits. During movement they rotate to adopt an alignment of least resistance. Excavations revealed thick ice lenses under the base of a boulder in winter, and emergent shear planes in frontal ridges. Rates of boulder movement average from zero to a few centimetres per year and are exponentially related to gradient. The differential thermal conductivity (diffusivity) of the boulder and surrounding soil implies that the seasonal freezing plane descends more rapidly through the boulder, causing ice‐lens growth at the boulder base; conversely, the thaw plane reaches the base of the boulder whilst the surrrounding soil is still frozen. A limit‐equilibrium model of boulder movement by gelifluction suggests that movement results from trapping of excess water under boulders during thaw, elevation of sub‐boulder porewater pressures to above‐hydrostatic levels and consequent reduction in shearing resistance at the base of the boulder. Movement is initiated by thaw of soil immediately downslope, but allows trapped water to escape, reducing porewater pressures and allowing stability to be regained. This model appears consistent with the observed characteristics, distribution and behaviour of ploughing boulders. Copyright © 2001 John Wiley & Sons, Ltd.

Thrust-related, diapiric, and extensional doming in a frontal orogenic wedge: example of the Montagne Noire, Southern French Hercynian Belt

The Montagne Noire, which is situated at the toe of the orogenic wedge of the French Massif Central South European Variscides, appears to be a well-suited area for studying the origin and evolution of middle to upper crustal domes adjacent to foreland basins. The data reported in the present paper show that the Montagne Noire dome is a particular type of basement-involved frontal culmination in an orogenic wedge and foreland basin system. This frontal culmination is characterized by a syn-contractional HT decompression recorded by clockwise PTt paths and widespread strata overturning in thrust and fold structures, which controlled the sedimentation in the adjacent foreland basin. These unusual characteristics are interpreted to be a result of the succession of thrusting, diapirism and extensional collapse. Antiformal stacking of syn-metamorphic thrust sheets controlled the first stages of the foreland basin development. Diapirism was essentially responsible for the HT decompression and widespread strata overturning. Extensional doming was a result of late- to post-metamorphic collapse acting on the pre-existing high-amplitude dome. Diapirism and associated isothermal decompression metamorphism, which constitute the essential difference between the Montagne Noire and ‘ordinary’ frontal ridges in orogenic wedges, were probably enhanced by a local partial melting of the upper to middle crust. It is suggested that the occurrence of these phenomena in front of an orogenic wedge was related to local over-thickening due to the superposition of an upper crustal antiformal stack on top of a lower crustal ramp anticline.

Skull development of the California sea lion (Zalophus californianus californianus)

This work describes the skull development in males and females of the California sea lion (Zalophus californianus californianus) examined in 87 specimens collected in the Gulf of California between 1982 and 1991. Forty-three measurements, nine qualitative characters and the number of upper-canine-tooth dentine layers, in addition to the natal layer, were recorded. Growth parameters were calculated with the von Bertalanffy equation and Cartesian distortions were used to schematize the skull development. To simplify the description of development, the skull was divided into the following parts: (1) braincase, (2) auditive apparatus, (3) masticatory apparatus and (4) nasal apparatus. Males with zero tooth dentine layers have skulls slightly smaller than those of females but they grow faster. Male skulls grow larger than those of females but the older males in the sample examined seem to have bone reduction. The most frontal ridge and sagittal crest are structures with evident asymmetry. Sexual dimorphism may be recognized in the skull proportions since birth. The female skulls grow fairly uniform I time, as well as in length and width. In the males, the skull grows more in length after birth and more in width thereafter. This heterogeneity is more marked in the masticatory apparatus. The capacity of bone remodeling in the different parts is not related to their degree of sexual dimorphism. The variation in the sample examined shows the need to study skulls developoment in relation to geographic and environmental variations, as well as in relation to the habits of the animals throughout their life.

Mass-balance variability as a base for interpreting ice-core data

The spatial extrapolation of data from ice cores depends on the complexity of the glacier system where the drilling site is located. The correlation between net mass balance, b n, of a specific point and of the whole glacier is different for each point. Analysis of net mass balance of Tuyuksu glacier in the Tien Shan, central Asia, confirms that the distribution of mass balance with height is more-or-less constant from year to year except in years with extreme values b n. Two types of “similarity” are described, additive and multiplicative. The “similarity” changes gradually from additive at the peripheral parts of the Tien Shan to multiplicative in the most continental central and eastern parts. Glacier mass-balance fluctuations of the frontal ridges are connected to the oscillations of accumulation and consequently to precipitation. Where the climate is more continental the mass-balance variability depends much more on the melting conditions than on accumulation. For the spatial interpretation of ice-core drilling results, a special analysis of “similarity type” is necessary. It allows the fixing of the spatial borders of the glacier system for which the dhilling site is representative.

Mass-balance variability as a base for interpreting ice-core data

The spatial extrapolation of data from ice cores depends on the complexity of the glacier system where the drilling site is located. The correlation between net mass balance, bn, of a specific point and of the whole glacier is different for each point. Analysis of net mass balance of Tuyuksu glacier in the Tien Shan, central Asia, confirms that the distribution of mass balance with height is more-or-less constant from year to year except in years with extreme values bn. Two types of “similarity” are described, additive and multiplicative. The “similarity” changes gradually from additive at the peripheral parts of the Tien Shan to multiplicative in the most continental central and eastern parts. Glacier mass-balance fluctuations of the frontal ridges are connected to the oscillations of accumulation and consequently to precipitation. Where the climate is more continental the mass-balance variability depends much more on the melting conditions than on accumulation. For the spatial interpretation of ice-core drilling results, a special analysis of “similarity type” is necessary. It allows the fixing of the spatial borders of the glacier system for which the dhilling site is representative.

Nature and tectonic setting of the southern Kermadec submarine arc volcanoes: An overview

The 1000-km long Kermadec subduction system (northern New Zealand), and adjacent Havre Trough back-arc basin, associated with the Pacific-Australian plate boundary, is an archetypal example of an active “island arc” convergent margin. Although the position and tectonic setting of the frontal arc is critical to understanding tectonism and magmatism within an arc-back-arc system, this has not been, unequivocally established for the Kermadec subduction system. Swath surveys from the 35°–37°S segment of the Kermadec system reveal that the frontal arc comprises seven large arc stratovolcanoes (Rumble II, III, IV, Silent II, Rumble V, Tangaroa, and Clark). The frontal arc continues south with the Whakatane volcano sited at the northern extremity of the Taupo Volcanic Zone. Of these eight volcanoes, the latter four are newly identified, and all have constructional volumes varying between 50 and 260 km 3. All of these arc edifices are sited 15–25 km west of the Kermadec frontal ridge. Bathymetric data similarly indicate that other Kermadec arc volcanoes between 32° and 35°S also lie west of the ridge axis, within the “back-arc” region, while north of 32°S the arc volcanoes lie along the frontal ridge. This apparent variation in the tectonic position of the frontal arc coincides with other changes in the morphology of the subduction system, north and south of 32°S, and as suggested by Pelletier and Dupont (1990), may reflect differences in the length of the underlying subducted slab. The 35°–37°S frontal arc segment is sited within 35–45 km of the present-day back-arc rift axis, and may control the initial loci of rift graben evolution. Sidescan imagery and seafloor photography of the southern Kermadec arc volcanoes reveal a complex volcanic stratigraphy with intertwined pillow lavas, proximal pillow breccias, highly vesicular scoriaceous lapilli, and pervasively mass-wasted volcaniclastic and epiclastic detritus. All volcanic deposits interdigitate with pelagic sediments. A single K-Ar dated andesite from Whakatane volcano suggests that the history of the present frontal arc may extend back to at least 0.77 Ma while Rumble III and V volcanoes are the major, although not exclusive, sites of geologically recent edifice construction. The historical acoustic record of southern Kermadec submarine eruptions since 1958 is now regarded as equivocal, with the July 1986 eruption of Rumble III the only unambiguous volcanic activity recorded in modern times.