Lost River - Karst Information Portal

2007 NSS Convention Guidebook
from glacial events in the Pleistocene. Erosional
history includes: (1) uplift and slow dissection
of the region in the late Tertiary, with the
formation of residuum down to the level of the
lower Mitchell Plain surface; (2) a slight rise in
base level with a halt at the level of the upper
Mitchell Plain surface where weathering and
erosion reduced most the Mitchell Plain to
base level; and. (3) finally renewed dissection
prior to Pleistocene glacial events.
A study of the karst features showed them
to be influenced by drainage from nonsoluble
landforms (Palmer, 1969, p 30). A line of
sinkholes can be seen that have been generated
by a stream heading on the impermeable area
of unconsolidated sediment to the east. Water
draining from outliers of the Crawford Upland
4
Figure 11. Mitchel Plain cross sections from Figure 10
(modified from M. Palmer, 1976).
has also initiated sinkhole development.
The largest remaining area of residuum and
unconsolidated sediment on the Mitchell Plain
is found in the Lost River area. Lost River, one of
the few east to west flowing rivers, drains this area
of unconsolidated material and sinks on contact
with bedrock to the west in a series of classic
swallow holes. Karst streams are continually
transporting unconsolidated material so that the
nonkarst area is gradually retreating.
Limestone areas lacking sinkholes in the
dissected area of the Mitchell Plain appear to
be identical in terms of geology to the large
sinkhole areas to the west: however, they
are not bounded by insoluble areas. Caves
underlying the sinkhole plain are fed by
recharge from the sinkholes. A few sinkholes
are abnormally deep
and represent collapse
sinkholes over active
stream passages.
If the sinkhole
bottom elevations
are contoured,
linear areas of very
low sinkholes stand
out. These generally
are over the active
cave systems, and
the “’lows” give an
approximation of the
cave potential in this
type of setting in the
southern Mitchell
Plain. Only a few
large caves have been
discovered here.
However, the large
number of linear
sinkhole trends
which appear to be
diagnostic of cave
development indicate
that the potential for
cave exploration in
the sinkhole plain has
hardly been touched.