Exploring linkages between coastal progradation rates and the El Niño Southern Oscillation, Southwest Washington, USA

Climate oscillations such as the El Niño-Southern Oscillation (ENSO) affect storm tracks, wave climate, precipitation and sea level in the U.S. Pacific Northwest. The impacts of these changes on coastal behavior have not been investigated in detail beyond the study of recent El Niño events, largely because existing historical records of coastal behavior are not of sufficient resolution to study annual responses to climatic forcing. We compare a newly developed annual record of coastal progradation for a location on the Washington coast, generated using high-resolution subsurface ground penetrating radar (GPR , with ENSO indices. This analysis reveals higher rates of seaward coastal growth following the warm, El Niño, ENSO phase and lower rates of coastal growth following the cold, La Niña, ENSO phase. The observed relationship between ENSO and progradation, although weak, is hypothesized to result from differences in sediment transport patterns and beach recovery rates following El Niño and La Niña events

Slipfaceless 'whaleback' dunes in a polar desert, Victoria Valley, Antarctica: Insights from ground penetrating radar

The Lower Victoria Valley is one of the McMurdo Dry Valleys, Antarctica, and has the largest concentration of aeolian sand dunes on the continent. Aeolian bedforms include elongate slipfaceless dunes which have been called ‘whaleback’ dunes. These dunes are composed of coarse sand and capped by granule ripples. Ground penetrating radar (GPR) profiles across one of these dunes reveal low-angle inclined sigmoid/tangential and convex reflections that are interpreted as strata within the dune. These dipping strata record the migration of the whaleback dune and show that they are not sand mantles as previously described but are actively migrating, long-wavelength, low-amplitude bedforms resembling zibar. An 800 m profile along the axis of the dune reveals low-angle dips from west to east showing that the dune has accreted towards the east. GPR profiles collected at 100 m intervals transverse to the dune axis reveal sets of cross-stratification dipping towards the south at the eastern end of the dune and towards the north at its western end. These apparent dips are resolved to show that the dune has migrated from west to east, driven by westerly foehn winds and katabatic winds blowing from the Polar ice cap, whilst at the same time it has been building obliquely towards the south. Accretion towards the north at the western end of the dune is attributed to reworking of the dune sand by easterly winds blowing inland from McMurdo Sound. An unconformity within the dune suggests that the wind regime has varied in the past. Beneath the unconformity the direction of dune migration was from west to east, and eastward extension of the dune continues at the present day. However, this is combined with accretion towards the north and west at the western end of the dune which is not recorded in the older sediments beneath the unconformity. Sand wedge structures that may have taken hundreds to thousands of years to form are found within the dune, and suggest that arid conditions suitable for dune construction have persisted in Victoria Valley for a considerable time

Stratigraphic imaging of the Navajo Sandstone using ground-penetrating radar

The geomorphic and stratigraphic variety within and among modern and ancient aeolian (wind blown) dune fields is an immense topic of research. Aeolian deposits form important petroleum reservoirs; examples include the large gas-bearing sandstones of the Permian Rotliengendes Formation beneath the North Sea, the Pennsylvanian-Permian Weber and Jurassic Nugget oil reservoirs of the overthrust belts of Colorado and Wyoming, respectively, and the oil-bearing Minnelusa Formation (Permian) reservoirs located in the Powder River Basin of Wyoming

Investigation of the age and migration of reversing dunes in Antarctica using GPR and OSL, with implications for GPR on Mars

GPR provides high resolution images of aeolian strata in frozen sand in the McMurdo Dry Valleys of Antarctica. The results have positive implications for potential GPR surveys of aeolian strata on Mars. Within the Lower Victoria Valley, seasonal changes in climate and a topographically-constrained wind regime result in significant wind reversals. As a consequence, dunes show reversing crest-lines and flattened dune crests. Ground-penetrating radar (GPR) surveys of the dunes reveal sets of cross-strata and low-angle bounding surfaces produced by reversing winds. Summer sand transport appears to be dominant and this is attributed to the seasonal increase in solar radiation. Solar radiation which heats the valley floor melts ice cements making sand available for transport. At the same time, solar heating of the valley floor generates easterly winds that transport the sand, contributing to the resultant westward dune migration. The location of the dune field along the northern edge of the Lower Victoria Valley provides some shelter from the powerful föehn and katabatic winds that sweep down the valley. Topographic steering of the winds along the valley and drag against the valley wall has probably aided the formation, migration and preservation of the dune field. Optically-stimulated luminescence (OSL) ages from dune deposits range from 0 to 1.3 kyr showing that the dune field has been present for at least 1000 yr. The OSL ages are used to calculate end-point migration rates of 0.05 to 1.3 m/yr, which are lower than migration rates reported from recent surveys of the Packard dunes and lower than similar-sized dunes in low-latitude deserts. The relatively low rates of migration are attributed to a combination of dune crest reversal under a bimodal wind regime and ice cement that reduces dune deflation and restricts sand entrainment

Beach volume on an eroding sand-gravel coast determined using ground penetrating radar

Mixed sand and gravel beaches form a wedge of protective sediment at the base of eroding cliffs. In profile these beaches are typically steep with a prominent storm berm. If the volume of beach sediment is insufficient, storms strip beach sediments seaward, exposing the cliff toe to wave attack. The beach volume is thus crucial to the protection of sea cliffs. In this article we describe a method of calculating alongshore variation in the volume of mixed sand and gravel beaches using ground penetrating radar (GPR). Eighteen sites were studied along 50 km of the east coast of South Island, New Zealand. The method was underpinned by an ability to map the boundary between beach sediments and underlying Pleistocene alluvial-fan sediments. This was achieved by studying the radar facies, particularly landward-dipping overwash deposits and seaward-dipping beach erosion surfaces. The method was ground-truthed in three ways: (1) a stream provided a clean section through one site that was imaged by radar; (2) a storm stripped beach sediment from three sites exposing the substrate, which was then surveyed and compared with radar profiles; (3) excavations in a previous study at nine sites were used to combine the stratigraphy with the radar images. GPR proved highly effective in this environment, revealing thin beaches in the south of the study area that thicken northward in the direction of alongshore sediment transport. Cliff height decreases northward such that there is a transition from beaches in front of cliffs, to beaches that overtop low cliffs, to barriers in front of a coastal lagoon

Internal structure of aeolian dunes in Abu Dhabi determined using ground penetrating radar

A ground‐penetrating radar survey of aeolian dunes in the Al Liwa area of Abu Dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures. The interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles. NNW— SSE‐orientated radar profiles, approximately parallel to the prevailing wind direction, show two sets of dipping reflectors which are interpreted as sets of cross‐stratification and second‐ and third‐order bounding surfaces. Radar profiles orientated WSW—ENE across the prevailing wind direction are dominated by concave‐up reflectors which are interpreted as trough‐shaped scours and sets of trough cross‐stratification produced by oblique progradation of barchanoid dunes. Nested troughs, with small sets of trough cross‐stratification within larger troughs, may be due to reactivation following wind reversal, or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes. Convex‐upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs. Overall there is a tendency for the larger second‐order bounding surfaces to dip downwind, which confirms Brookfield's ideas of the relative migration paths of dunes and draa