Absence of frost sorting at an experimental site, green lakes valley, colorado front range, usa

Abstract

A field experiment at 3,350 m.a.s.l. in the Colorado Alpine was initiated in 1959, to investigate frost sorting. Four plots, of varying grain-size composition, were used to test whether sorting by freeze-thaw activity could be related to the percentage of soil particles finer than 0.074 mm and whether there was a characteristic grain size at which lateral and/or vertical sorting could be expected. Re-examination of the site in 1984 indicated that macrofabrics, microfabrics, soil physical properties and surface clast distributions showed no evidence of large-scale sorting. Critical conditions for the onset of pore water convection, as a mechanism for the initiation of sorting, could occur in only two of the test soils (A and B), and permeability in the third (C) was too low to allow instability. Soil convection is also unlikely, owing to the coarse, freely drained nature of the test soils. Des conditions favorables au declenchement de phenomenes de convection contreles par l'eau des pores comme mecanisme responsable du triage pourraient seulement survenir dans deux des sols testes (A et B); la permeabilite du troisieme (C) etait trop faible pour permettre une instabilite. Une convection du sol est aussi improbable etant donne la nature grossiere et librement drainee des sols etudies.