The growth of snow bedforms

<p>Wind-blown snow does not lie flat. It self-organizes into dunes, waves, ripples, and anvil-shaped sastrugi. These features, called snow bedforms, are high-speed analogues of sand features barchans, ripples, and yardangs. Snow bedforms appear within hours or days after a blizzard, and may migrate as fast as several meters per hour. They are widespread, and affect the albedo and thermal properties of snow across the polar regions, but thus far they have attracted little attention within aeolian geomorphology.</p><p>For the past three winters, I have documented the growth of snow bedforms in Colorado Front Range. I present time-lapse footage showing the movement of snow dunes, ripples and sastrugi (see tinyurl.com/bedform-videos). These observations show that (1) snow is only flat when winds are slower than 6.4 m/s (2) snow dunes adjust minute-by-minute to changes in wind speed, (3) the most widespread bedform, sastrugi, evolve by migrating and eroding downwind, and (4) snow waves and dunes deposit layers of cohesive snow in their wakes, and thus aid snow deposition in windy conditions. These observations provide the basis for new conceptual models of bedform evolution based on the rates of snowfall, aeolian transport, erosion, and snow sintering across the snowscape.</p>

Searching for Non-Causal Explanations in a Sea of Causes

In the spirit of explanatory pluralism, this chapter argues that causal and non-causal explanations of a phenomenon are compatible, each being useful for bringing out different sorts of insights. First the chapter reviews the author’s model-based account of scientific explanation, which can accommodate causal and non-causal explanations alike. Then it distills from the literature an important core conception of non-causal explanation. This non-causal form of model-based explanation is illustrated using the example of how Earth scientists in a subfield known as aeolian geomorphology are explaining the formation of regularly-spaced sand ripples. The chapter concludes that even when it comes to everyday “medium-sized dry goods” such as sand ripples, where there is a complete causal story to be told, one can find examples of non-causal scientific explanations.

Of Meuse and Man: the geomorphogenetic and archaeological predictive maps of the Dutch Meuse valley

For the first time, geomorphology and archaeology are combined for a 165 km long stretch of the Meuse river, resulting in a geomorphogenetic map (GKM) and a series of archaeological predictive maps (AVM). The maps cover the central part the Meuse valley, located in the province of Limburg between Mook in the north and Eijsden in the south. The area consists of fluvial and aeolian landforms of the Holocene Meuse floodplain and Younger Dryas aged terraces along it, spanning a period of approximately 15,000 years of landscape genesis and human habitation. The GKM more clearly discriminates between map units of Younger Dryas and early Holocene age than in previous mappings of the Meuse valley. The AVM series provide predictive information on the location of sites for four distinct consecutive archaeological periods and four main cultural themes. The maps contribute to a better understanding of landscape processes (fluvial and aeolian geomorphology and the impact of man on river behaviour), and the possibilities for human habitation and land use in prehistoric and historic times.