Pillar Natural Arch
This type of natural arch is the result of cavity
merger. In this case, the cavities involved are two adjacent caves
or recesses whose backs have joined, leaving a remnant partition separating
the mouths of the caves. This partition is the lintel. Thus, the lintel
of a pillar natural arch is always vertical. There is a prone C-shaped
opening whose entrances are the mouths of the caves.
Miniature and minor pillar natural arches are very common. They are
frequently found in clusters. This striking configuration happens when
several adjacent recesses reach a vertical
joint that is close to and parallel with a cliff face. Preferential
erosion along the joint joins the backs of the recesses creating a series
of pillar natural arches that comes close to resembling a latticework.
Significant pillar natural arches are much rarer. Most are solitary,
but a few examples of clusters do exist.
The lintel of a pillar natural arch is seldom of structural importance
to the cavity behind it. If the lintel collapsed, it is unlikely that
the cave roof would also collapse as a result. The lintel is more fa�ade
than load bearing. Consequently, compression
strengthening seldom occurs. Thus, as erosion expands the cave,
the lintel just disappears. This is probably why few large examples
exist. It also implies that pillar natural arches have a relatively
A maturity attribute can be assigned based on the size of the lintel
in relationship to the opening. A young pillar natural arch has a lintel
breadth comparable to or larger than the horizontal extent of the entrances
adjacent to it. If the lintel breadth is much smaller than the entrances'
horizontal extents, the natural arch is an adult. If, in addition, the
lintel is highly scalloped or fractured, it can be considered old.