ALBERT

Description: 〈p〉Marine acoustic data are used to map and characterize submarine slope failure along the accretionary prism of Cascadia. Two main styles of slope failure are identified: (1) failures with curved head scarps, which are predominantly associated with incoherent debris-flow deposits; and (2) failures with rectangular head scarps, which are predominantly associated with intact sediment blocks. Rectangular head scarps mostly occur on thrust ridges with slope angles 〈/p〉

Description: Marine acoustic data are used to map and characterize submarine slope failure along the accretionary prism of Cascadia. Two main styles of slope failure are identified: (1) failures with curved head scarps, which are predominantly associated with incoherent debris-flow deposits; and (2) failures with rectangular head scarps, which are predominantly associated with intact sediment blocks. Rectangular head scarps mostly occur on thrust ridges with slope angles 〈16° and ridge heights 〈650 m, whereas curved head scarps occur predominantly on steeper and higher ridges. Off Vancouver Island, failure style and head-scarp geometry also change with ridge azimuth. We propose that the curved head scarps and debris flows may be a result of higher kinetic forcing of the downsliding sediments and a higher degree of mixing. At the more gently sloped, less elevated ridges, the kinetic forcing may be smaller, which leads to intact failure masses. Extensional faults at ridges with curved scarps may result from oversteepening and collapse of the sediments that cannot withstand their own weight due to limited internal shear strength. The slide geometries and potential controls on failure style may inform subsequent studies in assessing the risks for tsunami generation from submarine slope failures along the Cascadia margin.

Description: Multibeam bathymetric data acquired off Vancouver Island across the accretionary prism of the Cascadia subduction zone reveal a prominent segmentation of the deformation front with dominant azimuths of the ridges at ~120° and ~150° and abundant submarine landslides. Both these ridge-orientations are oblique to the direction of subduction (~45°). Ridges at a strike of ~120° show dominantly rectangular-shaped failure head-scarps and intact blocks of sediments within the failed sediment mass, whereas ridges with an azimuth of ~150° show curved head-scarps and incoherent debris in the failure mass. We propose that this systematic change in failure-style is related to the underlying thrust fault system producing steeper and taller ridges for azimuths around 150°, but less steep and tall ridges at 120°. Thus, debris-flow style failure is simply a result of higher kinetic forcing of the down-sliding sediment mass: more mixing and destruction of the coherent blocks for taller and steeper ridges, and blocks of intact sediment for gentle slopes and less elevated ridges. A segmentation of the deformation front and ridge alignment into two dominant azimuths could be a result of: a) complex interaction and competing forces from overall slab-pull (45°), b) re-activated faults orientated almost N-S (~175°) on the oceanic plate and overlying sediment cover (reflected in the magnetic stripes and abyssal plain strike-slip faulting), and c) relative orientation of the back-stop off Vancouver Island and accreted terranes (at ~127° following the coastline between Nootka Island and Port Renfrew). Extensional faulting is observed only at ridges with debris-flow style failure, which also are the ridges with larger height and steeper slopes. These extensional faults may be the result of over-steepening of the ridges and collapse of the sediment pile that can no longer withstand its own weight due to limited internal shear strength.

Description: Albedo plays a key role in regulating the absorption of solar radiation within ice surfaces and hence strongly regulates the production of meltwater. A combination of Landsat and Sentinel 2 data provides the longest continuous medium resolution (10–30 m) earth surface observatory records. An albedo product (harmonized satellite albedo, hereafter HSA) has already been developed and validated for the Greenland Ice Sheet (GrIS), using harmonized Landsat 4–8 and Sentinel 2 datasets. In this paper, the HSA was validated for various Arctic and alpine glaciers and ice caps using in situ measurements. We determine the optimal spatial window size in point-to-pixel analysis, the best practices in evaluating remote sensing algorithms with groundtruth data, and cross sensor comparison of the Landsat 9 (L9) and Landsat 8 (L8) data. The impact of the spatial window size on measured ice surface homogeneity and albedo validation was analysed at both local and regional scales. Homogeneity statistics calculated from the grey-level co-occurrence matrix (GLCM) suggest that the ice surface becomes more homogeneous as the image resolution becomes coarser. The optimal spatial window size was found to be 90 m, based on maximizing the statistical and graphical measures while minimizing the root mean square error and bias. HSAs generally agree closely with in situ albedo measurements (e.g. Pearson’s R ranges from 0.68 to 0.92) across various Arctic and alpine glaciers and ice caps. Cross sensor differences between L9 and L8 are minor, and we suggest that no harmonization is necessary to add L9 to our HSA product.