The Botanical Gardens at Asheville is a great place to visit in
order to see many varieties of plants native to the Southern
Appalachian Mountains. Admission is free and the gardens are open
from dawn to dusk every day of the year; please stay on the paths
and don't trample or remove the vegetation. And though while
visiting the gardens you can expect to see Witch Hazel, Trillium,
Bald Cypress, Saint John's Wort, and Azalea, you might be surprised
to find an EarthCache!
The term fold is used in geology when one or a stack of
originally flat and planar surfaces, such as sedimentary strata,
are bent or curved as a result of plastic (i.e., permanent)
deformation. Synsedimentary folds are those due to slumping of
material before deformation. Folds in rocks vary in size from
microscopic crinkles to mountain-sized folds. They occur singly as
isolated folds and in extensive fold trains of different sizes, on
a variety of scales. Folds form under varied conditions of stress,
hydrostatic pressure, pore pressure, and temperature - hydrothermal
gradient, as evidenced by their presence in soft sediments, the
full spectrum of metamorphic rocks, and even as primary flow
structures in some igneous rocks. A set of folds distributed on a
regional scale constitutes a fold belt, a common feature of
orogenic zones.
Major fold types include: Anticline (linear, strata dip away
from axial center, oldest strata in center); Syncline (linear,
strata dip toward axial center, youngest strata in center); Dome
(nonlinear, strata dip away from center in all directions, oldest
strata in center); Basin (nonlinear, strata dip toward center in
all directions, youngest strata in center); Monocline (linear,
strata dip in one direction between horizontal layers on each
side); Recumbent (linear, fold axis oriented at low angle resulting
in overturned strata below the fold axis); Slump (typically
monoclinal, result of differential compaction or dissolution during
sedimentation and lithification); and Ptygmatic (folds are chaotic,
random and disconnected, typical of sedimentary slump folding,
migmatites and decollement detachment zones).
Folding of rocks must balance the deformation of layers with the
conservation of volume in a rock mass. This occurs by several
mechanisms:
1. Flexural slip allows folding by creating
layer-parallel slip between the layers of the folded strata which,
altogether, result in deformation. The best analog is bending a
phone book, where volume preservation is accommodated by slip
between the pages of the book.
2. Typically, folding is thought to occur by simple buckling
of a planar surface and its confining volume. The volume change is
accommodated by layer parallel shortening the volume, which grows
in thickness. Folding under this mechanism is typically of the
similar fold style, as thinned limbs are shortened horizontally and
thickened hinges do so vertically.
3. Mass displacement. If the folding deformation cannot be
accommodated by flexural slip or buckling, the rocks are generally
removed from the path of the stress. This is achieved by pressure
dissolution, a form of metamorphic reaction, in which rocks shorten
by dissolving constituents which move to areas of lower strain.
Folds created in this way include examples in migmatites, and areas
with a strong axial planar cleavage.
At the listed coordinates you will find an
interesting fold formation. Your job is to come up with a
reasonable explanation for the forces and pressures that acted
upon this rock in order for it to look as it does. Email your
answer directly to me at ozguff@gmail.com and DO NOT include
this information in your online log. Also load a photo of you
and/or your group at the rock formation with at least one GPSr
included in the shot. Feel free to more fully tour the
gardens.
FTF HONORS GO TO
gotro&hc!!!
