Previous formation hypotheses
Scouring of the inner ejecta facies to form the grooves and deposition of the outer layer
[Schultz and Gault, 1979; Schultz, 1992; Mouginis-Mark, 1981; 1987; Boyce and MouginisMark, 2006] in the atmospheric, volatile-rich substrate, and base surge models is insufficient to
explain the formation of DLE craters due to observation that the inner layer overlies the outer
layer [Carr et al., 1977; Barlow and Perez, 2003; Osinski, 2011; Wulf et al., 2012]. Artemievia et
al. [2013] showed that impact melt is unlikely to overtop the rim (e.g. Osinski, [2006], Osinski et
al. [2011]), suggesting that this mechanism is not responsible for DLE formation. Regional
deflation of a subsurface ice sheet would also deplete ice underneath the ejecta deposit, and so
impact into subsurface ice layer [Senft and Stewart, 2008] fails to account for the classification
of many DLE craters as EE craters (e.g. Black and Stewart, [2008], Kadish and Head, [2011]).
Megablock distribution
Wulf et al. [2013] showed that the megablock distribution of the inner ejecta facies of the
fresh DLE crater, Steinheim (190.65°E, 54.57°N), to be radially oriented, in contrast to the outer
ejecta facies megablocks being concentrated in the distal ramparts of DLE craters [Wulf et al.,
2013] and SLE and MLE craters [Mouginis-Mark and Baloga, 2006]. Wulf et al. [2013]
concluded that this apparent block distribution is consistent with a laminar flow of the inner
ejecta facies, and granular flow/kinetic sieving for the outer ejecta facies (e.g. [Baratoux et al.,
2005; Baloga et al., 2005; Barnouin-Jha et al., 2005; Mouginis-Mark and Baloga, 2006; Wada
and Barnouin-Jha, 2006; Boyce et al., 2010]). Furthermore, they suggest that the broad nature of
the inner ejecta facies adjacent to the annulus indicates a relatively abrupt change in the ejecta
velocity. The apparent laminar flow of the inner ejecta facies inferred from the megablock
distribution by Wulf et al. [2013] is consistent with the apparent laminar nature of some
landslides (e.g. [Campbell et al., 1995]), and with our interpretation that the inner ejecta facies of
the DLE crater forms through a different process than the outer ejecta facies: a landslide of the
near-rim ejecta. We attribute the inferred abrupt change in velocity of the inner ejecta facies to
the decay of the structural uplift beyond 1.5 crater radii (R) [Settle and Head, 1977] and the
higher coefficient of friction (µ) value between the overthrusting inner ejecta facies on the outer
ejecta facies compared with the low µ between the near-rim ejecta and the underlying lubricating
glacial substrate.
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