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On December 22, 2018, the eruption and flank collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait causing catastrophic damage to uninhabited coastlines proximal to the source. Along the heavily populated shores of Banten and Lampung provinces in Java and Sumatra, tsunami waves caused severe damage, extensive inundation and more than 430 deaths. An international tsunami survey team (ITST) deployed 6 weeks after the event documented the tsunami effects including runup heights, flow depths and inundation distances, as well as sediment deposition patterns and impacts on infrastructure and the natural environment. The team also interviewed numerous eyewitnesses and educated residents about tsunami hazards. This ITST was the first to visit and document the extreme tsunami effects on the small islands in the Sunda Strait closest to Anak Krakatau (Rakata, Panjang, Sertung, Sebesi and Panaitan). Along the steep slopes of Rakata and Sertung islands, located less than 5 km from and facing directly towards the southwest flank of Anak Krakatau, all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m, while on the northeast tip of Sertung Island, facing away from the source, a single tree remained standing after flow depths of > 11 m above ground struck there. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest. This manifested as tsunami runup of < 10 m on Sebesi Island, located 15 km northeast of the source, contrasting with tsunami flow heights > 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the Ujung Kulon National Park, located 50 km to the south-southwest. Inundation and damage were mostly limited to within 400 m of the shoreline, likely the result of the relatively short wavelengths caused by the landslide generated tsunami. A significant variation in tsunami impact was observed along the shorelines of the Sunda Strait, with runup heights rapidly decreasing with distance from the inferred tsunami source. To model the event we applied a hot-start initial condition that roughly reproduced the measured tsunami runup heights along Rakata and Sertung. The waveforms were then propagated through the Sunda Straight using a Boussinesq-type wave model. The results showed a good fit to the observed heights along the Java and Sumatra coastlines, the northern coast of Panaitan Island and Ujung Kulon Nation Park. The model also produced an acceptable fit to the observed amplitudes at tide gauges. Despite the regional volcanic and tsunamigenic history of the region, and 6-months of eruptive activity prior to the event, the tsunami largely caught the local population off guard. This further highlights the need for community-based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis. [ABSTRACT FROM AUTHOR]

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation. [ABSTRACT FROM AUTHOR]

On 17 June 2017, a landslide-generated tsunami reached the village of Nuugaatsiaq, Greenland, leaving four persons missing and presumed dead. Here, we present a preliminary high-resolution analysis of the tsunamigenic landslide scar based on three-dimensional (3D) reconstructions of oblique aerial photographs taken during a post-failure reconnaissance helicopter overflight. Through a 3D quantitative comparison with pre-failure topography, we estimate that approximately 58 million m3 of rock and colluvium (talus) was mobilized during the landslide, 45 million m3 of which reached the fjord, resulting in a destructive tsunami. We classify this event as a “tsunamigenic extremely rapid rock avalanche,” which likely released along a pre-existing metamorphic fabric, bounded laterally by slope-scale faults. Further analysis is required to properly characterize this landslide and adjacent unstable slopes, and to better understand the tsunami generation. [ABSTRACT FROM AUTHOR]

SUMMARY On 2010 January 3 a moment magnitude MW 7.1 earthquake struck the Solomon Islands very near the San Cristobal trench, causing extensive landslides and surprisingly large tsunami waves. Because of the unique proximity of islands to the trench (<20 km) and earthquake, a post-seismic survey successfully identified unexpected widespread coseismic subsidence towards the trench (up to 80 cm), with no discernable post-seismic deformation. Approximately 1000 km from the earthquake ocean-bottom pressure sensors measured 1-2 cm open-ocean tsunami waves. Though spatially limited, the local tsunami wave heights up to 7 m were comparable to the much larger adjacent 2007 MW 8.1 earthquake. The seismically determined focal mechanism, broad-scale subsidence, tsunami amplitude and open ocean wave heights are all explained by an extremely shallow low-angle thrust adjacent to the impinging subduction of the two seamounts near the trench. This event belongs to a potentially new class of shallow 'tsunami earthquakes' that is not identified as deficient in radiated seismic energy. [ABSTRACT FROM AUTHOR]

On July 10, 1958, an earthquake Mw 8.3 along the Fairweather fault triggered a major subaerial landslide into Gilbert Inlet at the head of Lituya Bay on the southern coast of Alaska. The landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history. The mega-tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis. A cross section of Gilbert Inlet was rebuilt at 1:675 scale in a two-dimensional physical laboratory model based on the generalized Froude similarity. A pneumatic landslide tsunami generator was used to generate a high-speed granular slide with controlled impact characteristics. State-of-the-art laser measurement techniques such as particle image velocimetry (PIV) and laser distance sensors (LDS) were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup. The entire process of a high-speed granular landslide impact may be subdivided into two main stages: (a) Landslide impact and penetration with flow separation, cavity formation and wave generation, and (b) air cavity collapse with landslide run-out and debris detrainment causing massive phase mixing. Formation of a large air cavity — similar to an asteroid impact — in the back of the landslide is highlighted. A three-dimenional pneumatic landslide tsunami generator was designed, constructed and successfully deployed in the tsunami wave basin at OSU. The Lituya Bay landslide was reproduced in a three-dimensional physical model at 1:400 scale. The landslide surface velocities distribution was measured with PIV. The measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models. [ABSTRACT FROM AUTHOR]