Multi-temporal image analysis of very-high-resolution historical aerial and recent satellite imagery of the Ahnewetut Wetlands in Kobuk Valley National Park, Alaska, revealed the nature of thaw lake and polygonal terrain evolution over a 54-year period of record comprising two 27-year intervals . Using active-contouring-based change detection, high-precision orthorectification and co-registration and the normalized difference index, surface area expansion and contraction of 22 shallow water bodies, ranging in size from 0.09 to 179 ha, and the transition of ice-wedge polygons from a low-to a high-centered morphology were quantified. Total surface area decreased by only 0.4% during the first time interval, but decreased by 5.5% during the second time interval. Twelve water bodies (ten lakes and two ponds) were relatively stable with net surface area decreases of ≤10%, including four lakes that gained area during both time intervals, whereas ten water bodies (five lakes and five ponds) had surface area losses in excess of 10%, including two ponds that drained completely. Polygonal terrain remained relatively stable during the first time interval, but transformation of polygons from low-to high-centered was significant during the second time interval.
The dynamics of rock glaciers in marginal periglacial environments are poorly understood, especially in Eastern Europe where the enhanced continentality produces a distinct pattern of periglacial phenomena. Multi-temporal image analysis of high-resolution optical and radar satellite imagery of the Southern Carpathian Mountains, Romania revealed the small dynamic nature and a slow geomorphologic evolution of rock glaciers over a 46-yr period of record . Nine rock glaciers located in glacial cirques and troughs within the central area of Retezat Mountain were included in this study. Overall, the estimated displacement rates are extremely low (i.e., a few cm/year) compared with other active rock glaciers from all over the world. Despite their relative attenuated activity, it appears that Judele, Valea Rea, and Pietrele are still active rock glaciers, but in an evident disequilibrium/imbalance with the actual climate. These findings document the lowest altitude and easternmost active rock glaciers at this
Multitemporal satellite interferometric synthetic aperture radar (InSAR) techniques can characterize line-of-sight displacements of active landslide areas with resolution (mm scale) and accuracy comparable to or higher than differential GPS, sensor network, or photogrammetry techniques. This study improves understanding of the rate of movement and the lateral extent of the active domain of a landslide complex within Salmon Falls Creek Canyon near Twin Falls, Idaho. Specifically, we were able to estimate displacement of yearly motion rates in early and late stages of the event by analyzing a collection of archived radar satellite imagery. Small baseline subset (SBAS) InSAR performed better than persistent scatterer (PS) InSAR for analyzing distributed scatterers because of its ability to capture strongly nonlinear displacement rates. In addition, comparison with GPS field measurements showed agreement with InSAR-derived displacements.
Sunset Crater in north-central Arizona (USA) is a 900-year-old scoria-cone volcano. Wind action has redistributed its widespread tephra deposit into a variety of aeolian dune forms that serve as a terrestrial analog for similar landforms and aeolian processes on Mars. Fieldwork was conducted to collect essential geomorphological and sedimentological data, and to establish a baseline for the type and morphometry of dunes, physical properties, interactions with topography, and saltation pathways. Our analyses focused primarily on coppice dunes, falling dunes, wind ripples, and sand streaks. For all collected volcaniclastic aeolian sediment samples, the sand-size fraction dominated, ranging from almost 100% sand to 74.6% sand. No sample contained more than 1.6% silt. The composition is overwhelmingly basaltic with non-basaltic particles composing 2 to 6% of the total. Coppice (nebkha) dunes form where clumps of vegetation trap saltating particles and create small mounds or hummocks. Mean grain size for coppice dune samples is coarse sand. Measured dune height for 15 coppice dunes ranged from 0.3 to 3.3 m with a mean of 1 m. Mean length was 6.7 m and mean width was 4.8 m. Falling dunes identified in this study are poorly developed and thin, lacking a prominent ramp-like structure. Mean wavelength for three sets of measured ripples ranged from 22 to 36 cm. Sand streaks extend downwind for more than a kilometer and are up to 200 m in width. They commonly occur on the lee side of mesas and similar landforms and are typically the downwind continuation of falling dunes. Falling dunes, wind ripples, and sand streaks have been identified on Mars, while coppice dunes are similar to Martian shadow or lee dunes in which sand accumulates in the lee of obstacles.
This exploratory research used three sets of single polarized synthetic aperture radar (SAR) satellite data and a multi-temporal radar interferometry (InSAR) methodology to determine the spatial evolution and ground displacement trends of several industrial parks located in the metropolitan area of Bucharest, Romania.
The Newberry Springs Fault Zone experienced slip associated with the 1992 Landers earthquake in the Mojave Desert of California, USA. Detailed analysis of scaling relationships from single-event ground ruptures in the Newberry Springs Fault Zone mapped in the field shows an average maximum displacement to length (Dmax/L) relationship for fault segments (rupture lengths in the range of 100–1000 m) of 8×10−5–consistent with previously published Dmax/L ratios for normal fault earthquake ground ruptures (rupture lengths in the range of 1–100 km) of 7×10−5. To explore the ability of remote sensing (interferometric synthetic aperture radar or InSAR) to map small-displacement single-event fault ruptures and add constraints on segment displacements, we applied established interferometry methods with phase unwrapping to produce maps of line-of-sight displacement and displacement gradient. These maps highlight fault traces that experienced displacement during the time between collection of the synthetic aperture radar images. Comparison of published 1992 single-event ground rupture maps with mapping based on photogeologic interpretation of 1950s vintage aerial photographs indicates that most of the 1992 ruptures occurred as reactivation of pre-existing slip surfaces. In general, Dmax/L for total fault displacement is approximately 100 times Dmax/L for single-event ruptures. Evidence from the Newberry Springs Fault Zone indicates that, since the Pleistocene, at least 10–20 Landers-like slip events have occurred, reactivating the Newberry Springs Fault Zone. Evidence of wide damage zones and reactivation of individual segments developed in alluvial floodplain deposits, at relatively small (order of metres) fault displacements, supports a conceptual model of fault damage zone width being established early, during fault propagation. With continued displacement by accumulation of additional slip events, fault zone damage intensifies. The fault zone width may remain relatively stable, although the active portion of the fault zone will likely narrow as faulting continues and a throughgoing slip surface develops and accumulates the bulk of displacement.
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