Preeruptive flow focussing in dikes feeding historical pillow ridges on the Juan de Fuca and Gorda Ridges

Linear, hummocky pillow mound volcanism dominates at slow and intermediate spreading rate mid-ocean ridges. Volcanic hummocks are thought to be formed by low effusion rates or as a result of flow focussing during effusive fissure style eruptions in which the initial dike intercepts the seafloor and erupts along its entire length. In this study, high-resolution autonomous underwater vehicle (AUV) bathymetry is used to accurately map the extents of four historical fissure eruptions of the Juan de Fuca and Gorda ridges: on the North Gorda, North Cleft, and CoAxial ridge segments. The four mapped eruptions take the form of pillow mounds, which are similar in both lithology and dimension to hummocks on the Mid-Atlantic Ridge. Pillow mounds may be isolated, or coalesce to form composite mounds, aligned as ridges or as clustered groups. In three of the four mapped sites, the eruptions were discontinuous along their lengths, with pillow mounds and composite mounds commonly separated by areas of older seafloor. This style of discontinuous eruption is inconsistent with typical en echelon fissure eruptions and is probably due to a mildly overpressured, fingering dike intersecting the seafloor along parts of its length

The Cleft revealed: geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q04003, doi:10.1029/2005GC001038.The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been examined using high-resolution mapping systems, observations by remotely operated vehicle (ROV), ROV-mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping using multibeam (EM300) coupled with in situ observations that focused on near-axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley. The geochemically evolved and heterogeneous nature of these near-axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley. We suggest that the syntectonic capping volcanics observed off-axis were erupted from near-axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle.This research has been partially supported by a NSF grant to M. Perfit (OCE-0221541). M. Tivey acknowledges support from WHOI’s Mellon grant for Independent Study. Support for D. Stakes, T. Ramirez, D. Caress, and N. Maher and for the entire field program was provided by funds to MBARI from the Lucille and David Packard Foundation

Structure of Lo'ihi Seamount, Hawai'i and lava flow morphology from high-resolution mapping.

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Clague, D. A., Paduan, J. B., Caress, D. W., Moyer, C. L., Glazer, B. T., & Yoerger, D. R. Structure of Lo'ihi Seamount, Hawai'i and lava flow morphology from high-resolution mapping. Frontiers in Earth Science, 7, (2019):58, doi:10.3389/feart.2019.00058.The early development and growth of oceanic volcanoes that eventually grow to become ocean islands are poorly known. In Hawai‘i, the submarine Lō‘ihi Seamount provides the opportunity to determine the structure and growth of such a nascent oceanic island. High-resolution bathymetric data were collected using AUV Sentry at the summit and at two hydrothermal vent fields on the deep south rift of Lō‘ihi Seamount. The summit records a nested series of caldera and pit crater collapse events, uplift of one resurgent block, and eruptions that formed at least five low lava shields that shaped the summit. The earliest and largest caldera, formed ∼5900 years ago, bounds almost the entire summit plateau. The resurgent block was uplifted slightly more than 100 m and has a tilted surface with a dip of about 6.5° toward the SE. The resurgent block was then modified by collapse of a pit crater centered in the block that formed West Pit. The shallowest point on Lō‘ihi’s summit is 986 m deep and is located on the northwest edge of the resurgent block. Several collapse events culminated in formation of East Pit, and the final collapse formed Pele’s Pit in 1996. The nine mapped collapse and resurgent structures indicate the presence of a shallow crustal magma chamber, ranging from depths of ∼1 km to perhaps 2.5 km below the summit, and demonstrate that shallow sub-caldera magma reservoirs exist during the late pre-shield stage. On the deep south rift zone are young medium- to high-flux lava flows that likely erupted in 1996 and drained the shallow crustal magma chamber to trigger the collapse that formed Pele’s Pit. These low hummocky and channelized flows had molten cores and now host the FeMO hydrothermal field. The Shinkai Deep hydrothermal site is located among steep-sided hummocky flows that formed during low-flux eruptions. The Shinkai Ridge is most likely a coherent landslide block that originated on the east flank of Lō‘ihi.Funding for the collection of the data was provided by the National Science Foundation OCE1155756 to CM and the Schmidt Ocean Institute to BG. Support for DC and JP to process the data and write the manuscript was provided by a grant from the David and Lucile Packard Foundation to MBARI

Decision-making role preferences and information needs: a comparison of colorectal and breast cancer

Objective: An exploratory study has been carried out to examine decision-making role preferences and information needs for a sample of people with colorectal cancer (n = 48). The work replicated a larger study carried out for women with breast cancer (n = 150), and this paper compares and contrasts findings for both disease groups. Design: A cross-sectional design was employed, involving structured interviews. The main variables investigated were decision-making preference (using a decisional role preference card sort), perceived decisional role and information need (using an information needs questionnaire). Results: The majority (78%) of the colorectal cancer patients preferred to play a passive role in decision making, in contrast to 52% of women with breast cancer in previous work. Eighty per cent of the colorectal sample and 61% of the women with breast cancer perceived that the doctor had made treatment decisions. Priority information needs for both groups related to cure, spread of disease and treatment options. Conclusions: The two most striking findings from the comparison between the two disease groups relate to the differences in decision-making role preferences and the similarities in information needs. The process of involving people with colorectal cancer in treatment decision making warrants further investigation. The similarity in information needs of the two disease groups has implications for health care professionals providing information to people with cancer

Hydrothermal Chimney Distribution on the Endeavour Segment, Juan de Fuca Ridge

The Endeavour Segment of the Juan de Fuca Ridge is well known for its abundance of hydrothermal vents and chimneys. One‐meter scale multibeam mapping data collected by an autonomous undersea vehicle revealed 572 chimneys along the central 14 km of the segment, although only 47 are named and known to be active. Hydrothermal deposits are restricted to the axial graben and the near‐rims of the graben above a seismically mapped axial magma lens. The sparse eruptive activity on the segment during the last 4,300 years has not buried inactive chimneys, as occurs at more magmatically robust mid‐ocean ridges

Randomised feasibility study to compare the use of Therabite® with wooden spatulas to relieve and prevent trismus in patients with cancer of the head and neck.

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