Abstract
Abstract. Lobe and cleft patterns are frequently observed at the leading edge of gravity currents, including non-Boussinesq particle-laden currents such as powder snow avalanches. Despite the importance of the instability in driving air entrainment, little is known about its origin or the mechanisms behind its development. In this paper we seek to gain a better understanding of these mechanisms from a laboratory scale model of powder snow avalanches using lightweight granular material. The instability mechanisms in these flows appear to be a combination of those found in both homogeneous Boussinesq gravity currents and unsuspended granular flows, with the size of the granular particles playing a central role in determining the wavelength of the lobe and cleft pattern. When scaled by particle diameter a relationship between the Froude number and the wavelength of the lobe and cleft pattern is found, where the wavelength increases monotonically with the Froude number.
Highlights
This paper has presented experiments on the flows of fully suspended, lightweight granular material down an inclined surface
These currents have been found to exhibit characteristics of the instabilities found at the leading edge of both homogenous particle-laden gravity currents and flows of unsuspended granular material
During the early stages of motion a lobe and cleft instability mechanism, similar to that observed in homogenous particle-laden gravity currents, appears to be dominant
Summary
In this paper weDisseceukssionsmay in gravity play currents a role in and unsuspended granular powder snow avalanches. For homogenous Boussinesq gravity currents flowing a laboratory scale model of powder snow avalanches using along a horizontal surface a shifting pattern of lobes and lightweight granular material. When ulations (Hartel et al, 2000) have shown that the stagnation scaled by particle diameter a relationship between the Froude point at the front of a gravity current is located below the. The formation of the lobe and cleft pattern is the result monotoniDcalylynwaimth icsobfy a local instability at the leading edge the area of unstable stratification in of the the front caused flow region be-. In this paper we will refer to this instability as the classical lobe and
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