Abstract
Erosion of substrate materials by melting or mechanical means has
been suggested in active lava flows on Earth and other planets. Although
there are many references to lava erosion on Earth, unambiguous evidence
is rare; geological relationships commonly cited as evidence of downcutting
by lava can be explained without recourse to erosion. In order to
assess possible erosion by flowing lava we carried out field studies
of tube-fed basalt flows, sheet flows of the Columbia River Basalt
Province (CRB), and Precambrian komatiites. Unequivocal evidence
for thermal erosion (melted dacite substrate) was found at the Cave
Basalt lava tube, Mount St. Helens, for which fluid dynamic analysis
indicates laminar flow, although erosion was enhanced in areas of
locally steep slopes, possibly as a result of localized turbulence.
Other lava tubes in our study display strong, but inconclusive, evidence
for erosion. Komatiite flows display good evidence for erosion of
their substrate, possibly in a turbulent regime, but assessment of
the extent of erosion is hampered by limited and disrupted exposures.
No evidence for thermal erosion was found in the CRB. Our findings
suggest that an erosional origin for planetary sinuous rilles and
canali would be favored by high Reynolds number flows (high mass
flux, low-viscosity lava, steep slopes) and substrates having a lower
melting temperature than the lava or low mechanical strength (e.g.,
regolith).
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