Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska

An unstable rock slump, estimated at 5 to 10 × 10⁶ m³, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3–4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green’s law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours.     

Seasonal and spatial changes in the zooplankton community of Kongsfjorden, Svalbard

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m⁻³) was much lower than in the summer and autumn (410–10 560 individuals m⁻³). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.     

Suspended sediment source apportionment in Chesapeake Bay watershed using Bayesian chemical mass balance receptor modeling

A Bayesian chemical mass balance approach was used to estimate the contributions of potential sources into the suspended sediments in the Mill Stream, a tributary of Chesapeake Bay in Maryland, US. The Bayesian approach allows us to incorporate the uncertainties as a result of measurement errors in the elemental profiles of sources and suspended sediments in the stream and also the heterogeneities of the elemental profiles among samples into the analysis and provides us with probability densities representing the contribution of each source. Based on the obtained results, river bank erosion is the major source of sediments with a contribution estimated to range from 83% to 99% with a 95% credible interval. Also, a 95% credible interval in a range of 0.06% to 8% for cropland and 0.1% to 14% for forestland was provided. Hence, while the contribution of sediments from cropland or forestland cannot be ruled out, the model does not definitively demonstrate a significant contribution from either source. Copyright © 2012 John Wiley & Sons, Ltd.     

Giant palaeotsunami in Kiribati: Converging evidence from geology and oral history

For tsunami science within Oceania, the vast Central and Western Pacific (CEWEP) is an anomalous region because of the scarcity of historical tsunami observations and the complete absence of dated palaeotsunami evidence. This paper therefore records the first dated high-magnitude palaeotsunami event within the CEWEP region. A combination of both geological data and oral history is provided for a palaeotsunami that struck remote Makin island, northernmost of the Gilbert Islands in Kiribati, toward the end of the 16th century. A previously undocumented oral tradition of giant waves is well known to the people of Makin. Narration of this legend by the Wiin te Maneaba, traditional storyteller on Makin, provided important details supporting a tsunami hypothesis. The legend preserves credible information surrounding the giant-wave origin of Rebua and Tokia, two prominent subaerial megaclasts of blade and block geometry that were transported 80–130 m shorewards from the reef-edge source and deposited in sideways and inverted orientations. From available hydrodynamic flow transport equations, minimum flow velocities of 7.3–16.3 m s⁻¹ were generated, depending on whether the reefblocks were rotated or lifted onto the reef platform. The youngest U-Th age-dates for fossil corals retrieved from the reefblocks give a maximum age for the palaeotsunami of circa AD 1576. Several far-field Pacific Rim and regional possibilities exist for tsunamigenesis. These include subduction-zone seismicity and catastrophic volcanic eruption, both of which have been linked to earlier (late 15th century) palaeotsunami events recorded elsewhere in the Pacific Islands. However, the available evidence here suggests that the ~AD 1576 Makin palaeotsunami was more likely to have been locally generated by tsunamigenic offshore submarine slope failure close to Makin's western reef, associated with the giant arcuate bight structure that characterizes the northern rim of Butaritari atoll.     

Nonuniform cratering of the Moon and a revised crater chronology of the inner Solar System

We model the cratering of the Moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner Solar System, in order to refine the crater chronology method. Impact occurrences, locations, velocities and incidence angles are calculated semi-analytically, and scaling laws are used to convert impactor sizes into crater sizes. Our approach is generalizable to other moons or planets. The lunar cratering rate varies with both latitude and longitude: with respect to the global average, it is about 25% lower at (±65°N, 90°E) and larger by the same amount at the apex of motion (0°N, 90°W) for the present Earth-Moon separation. The measured size-frequency distributions of lunar craters are reconciled with the observed population of near-Earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith. Varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size-frequency distributions. We give a revised analytical relationship between the number of craters and the age of a lunar surface. For the inner planets, expected size-frequency crater distributions are calculated that account for differences in impact conditions, and the age of a few key geologic units is given. We estimate the Orientale and Caloris basins to be 3.73 Ga old, and the surface of Venus to be 240 Ma old. The terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 Ma. Better knowledge of the orbital dynamics, crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps, from the observation of asteroids to the formation of craters. Our model may be inaccurate for periods prior to 3.5 Ga because of a different impactor population, or for craters smaller than a few kilometers on Mars and Mercury, due to the presence of subsurface ice and to the abundance of large secondaries, respectively. Standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3.5 Ga ago, and give self-consistent estimates of the planetary cratering rates relative to the Moon.     

Mapping oil spill environmental sensitivity in Cardoso Island State Park and surroundings areas, São Paulo, Brazil

This study presents an environmental oil spill sensitivity map of Cardoso Island State Park, located in São Paulo state, Brazil, including some of its surrounding areas. This map was designed following the procedures determined by the Brazilian Federal Environment Organ (Ministry of the Environment), which separates coastal habitats in different littoral sensitivity indexes (LSI) to oil spills. We have also analysed some seasonal variations in morphologic and textural parameters at the local marine beaches that could affect their sensitivity, having found that they are more sensitive during summer due to a wider foreshore zone during these periods. Local most sensitive habitats are estuarine mangroves (LSI 10) and estuarine mud banks (LSI 9). Marine beaches were ranked LSI 3, and littoral rocky shores were subdivided in exposed flat rocky shores (LSI 1), boulder rocky shores (LSI 6) and sheltered rocky shores (LSI 8). Due to the elevated sensitivity of an estuarine system in the area, we considered necessary the installation of an Environmental Emergency Centre and the design of an emergency plan for the region in case of an accident resulting in oil spills within its vicinities.     

Hurricane-induced landslide activity on an alluvial fan along Meadow Run, Shenandoah Valley, Virginia (eastern USA)

Although intense rainfall and localized flooding occurred as Hurricane Isabel tracked inland northwestardly across the Blue Ridge Mountains of central Virginia on September 18–19, 2003, few landslides occurred. However, the hurricane reactivated a dormant landslide along a bluff of an incised alluvial fan along Meadow Run on the western flanks of the Blue Ridge Mountains. Subsequent monitoring showed retrogressive movement involving several landslide blocks for the next several months. Using dendrochronology, aerial photography, and stream discharge records revealed periods of landslide activity. The annual variation of growth rings on trees within the landslide suggested previous slope instability in 1937, 1972, 1993, 1997, and 1999, which correlated with periods of local flood events. The avulsive and migrating nature of Meadow Run, combined with strong erosional force potential during flood stages, indicates that landslides are common along the bluff-channel bank interface, locally posing landslide hazards to relatively few structures within this farming region.