Saturday, 6 November 2010 saw the geology club take a field trip to southeastern Ohio, to the scenic Hocking Hills (Hocking Hills State Park).  First on the itinerary was Old Man’s Cave and its associated gorge and waterfall.  After lunch, the group headed to Rock House.



Old Man’s Cave area


Near-vertical, vertical, and even overhanging sandstone cliffs occur along a stream gorge in the Old Man’s Cave area.  The main geologic scenery is the Black Hand Sandstone.


Old Man’s Cave



Gorge just upstream from Old Man’s Cave.  The dominant direction of creek erosion is downward.  The rocks making up the walls of the gorge are relatively resistant, planar-bedded to cross-bedded quartzose sandstones, pebbly sandstones, and conglomeratic sandstones of the Black Hand Sandstone.  The Black Hand Sandstone is ~mid-Early Mississippian in age (late Kinderhookian or early Osagean Stages).  It is traditionally interpreted as a delta deposit, but in recent years has been shown to be an ancient incised valley fill deposit.



Old Man’s Cave - the overhanging sandstone cliff that the group is looking at is Old Man’s Cave itself.  The rocks are part of the Black Hand Sandstone.



Waterfall a little downstream from Old Man’s Cave.  This visit was during a time of low flow in the stream, so the waterfall was a mere trickle.



Rock House area


Differential weathering and erosion of jointed Black Hand Sandstone has resulted in a “cave” along a cliff face called Rock House.  The only chamber extends parallel to the exterior cliff face  Several side openings (keyholes entrances) are present that connect the chamber with the cliff face.


OSUN Geology Club at Rock House



Rock House - the “cave” known as Rock House is behind & parallel to this cliff face, to the left of the viewer.  The rocks are dominated by planar-bedded and cross-bedded quartzose sandstones of the Black Hand Sandstone, an ancient incised valley fill deposit of ~mid-Early Mississippian age.



Rock House - one of several entrances to the chamber.  Rock House is not a true cave.  Nowhere in the cave can one get beyond twilight (= one of the criteria for true caves).  Most caves are the result of partial dissolution of limestones.  The bedrock here is principally quartzose sandstone (Black Hand Sandstone).  The greenish coloration is due to the presence of living algae on the surface of the rocks.  The red coloration is due to hematite staining (Fe2O3).



Rock House - the long axis of this chamber (~along the viewing direction) is developed along a major joint surface (easily seen in the ceiling) in the Black Hand Sandstone.  Differential erosion has significantly enlarged the joint plane, resulting in a “cave” big enough to walk through.  Several side openings (along the right wall as one view this photo) are developed along joint surfaces roughly perpendicular to the main chamber fracture.

Rock House has been recently cited as an Earth analogue to a type of cave that may be present on Mars.  If life evolved on Mars, and if that life still exists, it would have to be in the subsurface, most likely in cryptic environments or “refugia” such as caves.  Mars has lava tube caves (collapsed and non-collapsed) as well as overhang caves and crevice caves.  Rock House in the Hocking Hills of Ohio has been mentioned by planetary geologists as the kind of cave that future astronauts might explore on Mars in search of life.



Honeycomb Weathering - many Black Hand Sandstone outcrop surfaces have well-developed honeycomb weathering, formed by small-scale differential weathering and erosion.  The shaded, subvertical feature on the left side of the photo is one of numerous joints (fractures) in the Black Hand Ss.  The greenish & pale coloration on the rock surface is from the presence of living algae and lichen.



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