Mount Rushmore

The comments of a friend who works for the National Park Service are
below.  The comments are her opinion and do not necessarily
represent the position of the NPS.

Simon Barcham Green <simongreen [at] aol__com> writes

>N.J. Bud Goldstone <budgoldstone [at] yahoo__com> writes
>
>>I do believe we may lose chunks of our one-of-a-kind mountain
>>sculpture Mt. Rushmore to an unsafe "cleaning" operation. I don't
>>know why high pressure wound up as the selected method other than it
>>may have been the low bid, but my database says cleaning off lichen
>>and mold should be done with a simple, cheap wash job. What was the
>>the scientific backup that showed a blast was the way to go? Anyone
>>know?
>
>I don't know the answer to Bud Goldstone but I wondered why lichen
>and mold are considered a problem on a mountain sized sculpture.
>They may contribute marginally to biochemical erosion but could have
>some beneficial effects against  weather too. Like Bud I would be
>interested to know what technical and conservation assessment was
>made. Does small loss of rock within this scale matter?

I would guess that the plant life is a problem for 2 reasons:

    1.  The mold and lichens discolor the stone.

    2.  Other plant roots penetrate the stone, they open up little
        cracks for water to get in. The freeze thaw cycle would,
        over time, make the cracks bigger and ultimately lead to
        more problems, greater cracks, etc.

The idea of a "mountain size" sculpture not being susceptible to
these things is funny. After all, plant roots and the freeze thaw
cycle have helped to break rocks down into smaller rocks for time
immemorial. It would seem that "small loss" of rock on this scale
would ultimately lead to larger loss of rock.

To me, the question is why "high pressure" and not "low pressure"
but it may be less of an issue for the hard rock of Mt. Rushmore
than say, brick surfaces. Either way, the project would have had to
go through Section 106 Clearance with the State Historic
Preservation Office (it seems unlikely that a cleaning like this
which isn't done often would be considered "routine" and therefore
excluded from consultation with the SHPO.

Deborah Confer
Anthropology Collection Manager
University of Colorado Museum of Natural History
UCB 218
Boulder, CO  80309-0218
303-492-2198
Fax: 303-492-4195


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                  Conservation DistList Instance 19:7
                  Distributed: Thursday, July 21, 2005
                        Message Id: cdl-19-7-013
                                  ***