Abstract We describe and compare the morphology and activity of two types of gullies with different orientations collocated on the Kaiser dune field in the southern hemisphere of Mars: large apron gullies and linear dune gullies. The activity of large apron gullies follows an annual cycle: (i) material collapse into the alcove (mid-autumn/late winter) as CO 2 condenses; (ii) remobilization by mass flows (late winter); and (iii) continuous appearance of hundreds of ‘digitate flows’ on the fan (autumn/winter). We find that large apron gullies could form in hundreds of Martian years. In contrast, linear dune gullies are active briefly in late winter, when the CO 2 frost disappears. Their activity is characterized by the extension of channels, the creation of pits and the darkening of the surface. Linear dune gullies are likely to form within one to tens of Martian years. We infer that insolation, which influences the depth to ground ice and the amount of volatile deposited, may be the factor differentiating large apron gullies and linear dune gullies. Sediment transport by CO 2 sublimation is a good candidate for the activity observed in all of these features. However, linear gullies could also be formed by brine release when the temperature rises abruptly after the removal of the CO 2 ice.

ABSTRACT The Indiana Dunes is a name commonly used for the eastern part of the Calumet Lacustrine Plain, generally referring to the large dunes along the coast from Gary, Indiana, eastward to the Michigan state line. However, the Calumet Lacustrine Plain also contains complex coastal landscapes associated with late Wisconsin to Holocene phases of ancestral Lake Michigan (e.g., mainland-attached beaches, barrier beaches, spits), including those formed during quasi-periodic decadal and shorter-term waterlevel variability that characterize modern Lake Michigan (e.g., beach ridges, dunes, interdunal wetlands). Major industrial development and other human activities have impacted the Calumet Lacustrine Plain, often altering these landscapes beyond recognition. Today, geological and paleoenvironmental data are sought to inform regional environmental restoration and management efforts and to increase the resiliency of the coastal landscape to ongoing disturbances. During this field trip, we will examine the relict shorelines and their associated nearshore and onshore features and deposits across the Indiana portion of the Calumet Lacustrine Plain. These features and deposits record the dynamic interaction between coastal processes of Lake Michigan, lake-level change, and long-term longshore sediment transport during the past 15,000 yr. Participants will examine the modern beach, the extensive beach-ridge record of the Tolleston Beach strandplain, a relict dune field, and the large dunes of the modern shoreline, including Mount Baldy. At Mount Baldy, we will focus on the landscape response to human modification of the shoreline. We will also explore the science behind dune decomposition chimneys—collapse features that caused a 6-yr-old boy to become buried more than 3.5 m below the dune surface in 2013 and highlighted a previously unrecognized geologic hazard.

During 2004–2010, we studied the sand dunes of Oman using trenches, optically stimulated luminescence age dating, and modern wind data. This work was undertaken for Petroleum Development Oman to define modern analogs for ancient dune reservoirs that produce oil and gas in the sultanate. An unintended consequence of our work was the recognition of a band of high wind energy along the east coast of Oman that might be suitable for commercial wind power extraction, especially during the peak wind season of the Indian monsoon. Our geological work indicates that this basic wind regime has been in place for at least 200,000 yr and is thus not a fluke of present-day climate.

Abstract Eolian dune fields self-organize through a hierarchy of autogenic processes that culminate at the dune-field pattern level. Interactions that occur between flow and grains, flow and dunes, and dunes and dunes define the levels of this hierarchy. These autogenic processes occur within sets of boundary conditions, which impart a uniqueness to each emergent dune-field pattern. The interpretation of allogenic forcing on dune-field patterns and their stratigraphic record requires an understanding of how these external environmental variables are manifested at the dune-field pattern level. The fundamental process in eolian systems is a wind event with basic boundary conditions of sediment supply, sediment availability, and the transport capacity of the wind. It is hypothesized that the basic high-frequency boundary conditions are remade at each level of the hierarchy of autogenic processes or have a cumulative effect over many wind events. The influence of these boundary conditions “trickles up” to and is manifested at the dune-field pattern level. Tectonic, climatic and hydrologic boundary conditions are low frequency and operate over much longer timescales than a wind event. It is hypothesized that these “trickle down” to be remade as high-frequency boundary conditions, which then trickle up. Analysis of the White Sands Dune Field in New Mexico supports these hypotheses by the manifestation of the influence of boundary conditions in the dune-field pattern. The dune field originated by wind deflation of a lacustrine sediment supply, which was made available episodically by climatic forcing that controlled the hydrodynamics of the tectonic basin. Although the dune-field pattern arose through autogenic dune interactions, the morphologies of which are ubiquitous throughout the field, the influence of boundary conditions is evident in the dune morphologies and field-scale pattern heterogeneity.

Abstract A new map, the first based on interpretation of satellite imagery, reveals both the complexity of Australia's dunefields and their relationships with topography, climate and substrate. Of the five main sand seas, the Mallee, Strzelecki and Simpson in eastern Australia cover Quaternary sedimentary basins whereas the Great Victoria and Great Sandy dunefields in the west are formed by reworking of valley and piedmont sediments in a non-basinal landscape of low-relief ridge and valley topography. These dunefields cover large areas of the arid zone and semi-arid zone and small areas of dunes in sub-humid areas around the margins of the continent reflecting past expansion of arid climates during glacial stages of the last several glacial cycles. Several areas of low relief stand out as being largely dune-free: the limestone Nullarbor Plain, clay plains of the Georgina Basin and floodplains of rivers in the Carpentaria, Lake Eyre and Murray–Darling drainage basins where sand is rare or not transported by diminished Late Quaternary rivers. The Yilgarn Block of southwestern Australia is also surprisingly free of dunes, possibly as a result of long, deep weathering. Everywhere the history of climate change is evident in dune morphology and distribution, including large areas where the sand dune orientations are markedly divergent from modern sand moving wind directions.