Mltiple mountain ranges form multiple rain- shadows near and far from a coast with moist incoming winds. This creates a great variability in water available to life and so creates many diverse habitats especially when combined with many rock types (read the text box to the right. The Klamaths are a patchwork of folded and faulted, metamorphosed rocks and intruded igneous rocks . Displaced rocks masses with a shared history (terranes) were pushed, shoved, squeezed, and heated. Continental and oceanic plates collided and in the process, the seafloor slabs were “plastered” against or scraped off upon the continental face like frosting on a knife dragged across a chocolate cake. Currerntly the an oceanic plate slides below to melt and rise as the volcanoes of the Cascade Mountains. Granites, diorite, gabbro, and ultramafic rocks are the harder mountain-forming rocks with limestone, shale, sandstone, chert, and recent sediments like gravels adding to the variety. John Whetten, noted Northwest geologist, aptly described such complex mélanges as “fruit-cake geology,” in contrast to the self-evident “layer cake geology” of the Columbia Plateau of Washington State. What’s so special about the Klamaths? Rock types in the Klamaths accumulated onto one another over time, like a growing shelf of different books. Today, the ‘terranes’ as they are called are tilted, allowing more of each rock type to be exposed in more locations on the surface. More exposure
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Transcript
Mltiple mountain ranges form multiple rain-
shadows near and far from a coast with moist
incoming winds. This creates a great variability in
water available to life and so creates many
diverse habitats especially when combined with
many rock types (read the text box to the right.
The Klamaths are a patchwork of folded and
faulted, metamorphosed rocks and intruded
igneous rocks . Displaced rocks masses with a
shared history (terranes) were pushed, shoved,
squeezed, and heated. Continental and oceanic
plates collided and in the process, the seafloor
slabs were “plastered” against or scraped off upon
the continental face like frosting on a knife
dragged across a chocolate cake. Currerntly the an
oceanic plate slides below to melt and rise as the
volcanoes of the Cascade Mountains.
Granites, diorite, gabbro, and ultramafic rocks are
the harder mountain-forming rocks with
limestone, shale, sandstone, chert, and recent
sediments like gravels adding to the variety. John
Whetten, noted Northwest geologist, aptly
described such complex mélanges as “fruit-cake
geology,” in contrast to the self-evident “layer
cake geology” of the Columbia Plateau of
Washington State.
What’s so special about the Klamaths?
Rock types in the Klamaths accumulated onto one another
over time, like a growing shelf of different books.
Today, the ‘terranes’ as they are called are tilted, allowing
more of each rock type to be exposed in more locations on
the surface.
More exposure
How did the cave form?
Cave Guide Compiled by Gina Roberti,
GeoCorps 2014-2015.
Document stored in the O:drive. Titled
‘Cave Guide With Pictures’ saved in
Interpretation Questions.Answers folder.
For more detailed geologic information
about the cave, see most recent “Room
by Room Cave Guide” (by John Roth).
CRACKS
three types of cracks at Oregon Caves
allow water to percolate into the marble (a
relatively impermeable rock) allowing cave
passages to grow
JOINTS
near surface
steep cracks
formed as
overlying rocks
erode away,
releasing
pressure and
allowing the
marble to
expand
FAULTS
a fracture or discontinuity
in a rock along which
slippage has occurred There are two types of faults
in geology, normal and thrust
(reverse).
Geology Sidebar: Normal vs. Reverse Faults Faults occur at different geometries depending on the
relative compression or extensional forces acting upon the
rocks.
extension compression
PARTINGS
Cracks between
different rock layers
formed because each
layer responds
differently to pressure,
temperature, like
cracks between bricks
and mortar in old
buildings
Rooms can also form when one rock layer slides over another (for example a normal fault), movement and rock slip crushes rock along the fault plane and thus allow more water to flow through, further expanding the crack
Oregon Caves:: a developed cave with ~3 miles of surveyed length, under some 8 acres
one crack
makes a
passage
intersecting cracks
more likely makes
a room
Parting and fault in the Dry Room
Belly of the Whale
examples of how cave rooms and orientation of passages are controlled by where cracks (faults and joints) run
CO
2
CO
2
CO
2 CO
CO
2 CO
2
CO
2 CO
2
CO
2
CO
2
CO
2
DIFFUSION GRADIENT:
greater concentration of carbon
dioxide in closed container than
surrounding air.
Degassing of CO2 causes
carbonated drinks to ‘fizz’.
This same process happens in
the cave. When the CO2
‘fizzes’ off, the amount of
carbonic acid drops, Calcite
then comes out of solution and
is deposited in cave formations.
Since carbonic acid keeps calcite in solution, anything that
reduces carbonic acid will result in the deposition of
calcite (if the solution is saturated with calcite). You can
get that fizz by opening a bottle of carbonated water or by
evaporation, shaking, or heat after the bottle is opened. All
this releases carbon dioxide from within the water, to
areas outside the water - where the amount of carbon
dioxide is less - in what is called a diffusion gradient.
The concentration of CO2 in the air determines
whether water saturated with CO2 will dissolve or
precipitate calcite. The greater the difference between
the concentration of calcite in the air with respect to
the water (the concentration gradient), the more likely
carbon dioxide in the water will degas and dump
calcite. This is why the most calcite is precipitated just
beyond the freeze-thaw zone near entrances as the
amount of carbon dioxide is less there than in the rest
of a cave. This includes the Petrified Forest and
Niagara Falls of the Caves
This same process occurs when a person "cracks"
their knuckles by reducing joint pressure:
The sound of the knuckles cracking is from tiny
carbon dioxide bubbles forming.. You can’t crack
your knuckles again for at least a few minutes,
because it takes that long for the carbon dioxide to
re-dissolve back into the fluids of your joints.
Most loss of carbon dioxide in water
entering a cave occurs because the
water has up to a 100 times more
carbon dioxide than cave air does.
Evaporation can increase the diffusion of
carbon dioxide from water into cave air
because it concentrates the remaining
carbon dioxide in the water and thereby
increases the diffusion gradient.
Water containing the highest
amounts of CO2 have the
maximum potential to dissolve
calcite (CaCO2).
As it gets more saturated with
calcite it can dissolve less and
less
Thus, new waters entering the
cave that have flowed mainly
through the soil above without
yet reaching the marble have
the maximum ability to dissolve
calcite especially if they have
flowed through soils not
developed on marble and
therefore didn’t pick up much
calcite.
As water moves through the cave
system, the concentration of
dissolved calcite and carbon
dioxide changes. This determines
whether cave is ‘growing’ or not in
certain areas.
Shelfstone layered calcite deposits.
Spitting Stone.
Dissolution and Precipitation
Cave Formations
Large crystals require space
and time to grow!
In marble caves, limestone
formations are formed from the
re-precipitated dissolved calcite
from marble.
Both limestone and marble
are made of the same
mineral, calcite.
‘fat’ versus ‘thin’ speleothems
indicate past climates or waterflow
pathway length
speleothems vs. speleogens secondary
limestone
deposits, such
as stalactites,
flowstone, cave
popcorn, etc.
features created from the removal
of material such as rills, relief
features on walls or ceilings, etc.
thin: broomstick
dry climate &/or
long water pathway
(slow drip, waters
saturated in calcite
which precipitates
out even as running
along the column) fat: ice cream cone
wet climate (splatter) or moderately
long waterflow pathway
broomstick
Calcite crystals, ORCA. Photo by John Roth.
flowstone draperies
broomstick
(sometimes
analyzing
shapes is
easier than
analyzing
isotopes!)
cross section of broken stalactites
graphite graffiti (pencil signatures)
on flowstone now sealed in place
by an overlying layer of calcite
famously, an entire visiting geology
class signed their names along
with their professor
cave bacon, a cave drapery formed when
calcite is deposited with different amounts of
organics or, (more rarely), iron oxides
Larger crystals grow in stable conditions,
where they have space and time to grow.
Minerals prefer to form large crystals,
which are thermodynamically more stable
than smaller crystals, but conditions are
not always perfect to facilitate such
growth!
Smaller crystals form when conditions are
unstable. For example, cave popcorn is
common near cave entrances where
temperatures fluctuate over seasons.
Conditions around new openings
especially change quickly.
Cave popcorn is a type of ‘coralloid’
(rounded balls) formation. Popcorn can
forms from cycles of rapid wetting and
evaporation- changing conditions too
quickly. Calcite is deposited each time the
water evaporates away or carbon dioxide
is lost rapidly.
Cave Popcorn, ORCA.
Certain formations are characteristic of specific conditions. Most soda straws form closest to the surface, fed by water flowing through joints and faults (cracks). Vertical joints and faults both open near the surface with the loss of overburdening pressure, but deeper down, joints remain closed. Dripstone develops deeper in the cave along a few vertical faults that are fed by many joints before they peter out. Hence the stalagmites and stalactites are fewer in number but bigger deeper down, as in Miller’s Chapel.
soda straws with cave popcorn forming on top, indicating changing depositional conditions
(temperature fluxuations, water flow, dissolution capacity of water) in this section of the cave
CAVE FORMATIONS continued.
Cave popcorn usually forms
through loss of carbon
dioxide but near entrances
can also be from evporation.
Cold air, especially during
winters, nights, and glacial
periods, flows into the cave.
As it moves into the cave, the
air warms up and is therefore
able to evaporate more water.
This air is, relative to other
cave air, lower in carbon
dioxide. Therefore, more
carbon dioxide is going to be
lost to this air from water in
the cave in order to equalize
the difference.
Calcite crystals and
soda straws, ORCA.
Radiometric Dating How old are formations in the cave?
How do we know?
Multiple means of dating.
(2)
Thorium and Uranium are two
radioactive minerals common
in calcite used for radiometric
dating.
One is soluble (Uranium), one
insoluble (Thorium).
Thus in conditions near the
surface of the Earth, minerals
developing from waters with
dissolved calcite will be 100%
saturated in the soluble ion
(uranium) but contain no
thorium.
BUT, over time, Uranium
breaks down into Thorium. at a
steady, known rate.
The change (or delta Δ) in the
ration of these two minerals
can be measured over time.
(1)
Carbon and oxygen isotopic record can
be used for radiometric dating as far
back as 300,000 years.
Carbon 14 dating (radiometric dating)
through carbon in organic matter
(bones) is possible...but bones are not
great for dating; they are made of
material that is permeable and porous.
Yet paleontological analysis of various
critters preserved in the cave (jaguars,
bears) give time constraints on when
certain passages must have been open.
How old is the main cave at Oregon Caves?
Based on the radiometric and oxygen isotope age
determined by Dr. Turgeon, the oldest speleothem
(secondary formation) in the cave is about half a million
years old. Based on relatively fast erosion of caves in
steep sided mountains, that means the cave itself
probably is somewhere from half to several million
years old.
(We say ‘main cave’ because there are other smaller cave
systems on the Monument and Preserve as well as in the
region, including the Marble Mountains in Northern
California.)
How long does it take to form large caves?
With a width of about 100 feet, large rooms like the
Ghost room may have taken about 100,000 years to form.
The oldest known caves are very large caves with many
multiple levels (such as Mammoth Cave) or caves that
form very deep underground (such as Jewel Cave and
Carlsbad Caverns). Sections of these caves range from a
few million to tens of millions of years old. Scientists
estimate it takes about ten thousand years to develop big
enough holes in limestone that people can crawl through.
Marble, as a ‘harder’ metamorphic rock, takes even
longer to dissolve.
Measuring the ratio of
the thorium and uranium
gives the age of the
flowstone, the oldest
date at ORCA at about
330,000 years. In older
layers in the Cave,
there's not enough
uranium in the rock to
date it by this method
alone. Instead, oxygen
and carbon isotope
ratios can be matched to
ratios in ocean cores.
Using this method it was
calculated that
speleothems in Oregon
Caves began forming
about 516,000 years ago.
Most cave formations are impervious to
water, which .make them good for dating.
Photograph of stalagmite from Oregon Caves
National Monument, parallel to the growth
direction. Black ovals are centered at sites
sampled for U-Th dating. Scale bar (length of
stalagmite) is 26.5 cm. This sample was taken
from the cave in 1930 and analyzed in 2000.
Source: Vacco 2005
What can be read from a speleothem? Speleothems are important archives of
terrestrial paleoclimate (changes in climate
on the Earth’s surface over geologic time).
They preserve detailed environmental
records derived from chemical and isotopic
proxies that can be precisely dated.
Changes in speleothem growth provide an important
constraint on paleoenvironmental conditions
because speleothem formation requires both water
and CO2, changes in which can reflect rates of
respiration (decomposition) in the soil zone above
the cave, which in turn are dependent on local
precipitation and temperature conditions.
How fast do stalactites grow?
The simple answer is about 1 inch per 1000
years. (Keeping in mind that it fluctuates widely over time
and depending on location in the cave.)
Actively forming soda straws in Oregon
Caves grow about a tenth of an inch to an
inch per one thousand years.
The flowstone and dripstone sampled by
Turgeon (2001) in Oregon Caves showed
growth rates between 1-32 millimeters per
thousand years during early to mid-
interglacial periods of the last 500,000 years.
A research project in 2005 found a growth
rate of 8.5 to 20 mm (.3”-.79”) per 1000 years
in the period during the last ice age and ~13.5
to 9.5” per 1000 years in the current
interglacial period, indicating faster growth
during interglacials compared to glacial
periods.
Since <1% of the soda straws in Oregon
Caves show any regrowth, the average is
<.0014”/century or around .015” (.032mm)
per 1,000 years. Growth has slowed down in
this interglacial compared to previous ones,
perhaps because it is a bit drier.
Figure 2.3. Results of cave temperature modeling
for the last 100 ka. The stippled line represents
the adjusted SST record (see text for explanation)
and the continuous line shows the average
temperature of the model runs that produced
modern cave temperatures of 7 to 8.8oC. The
shaded gray area represents one standard
deviation of the average modeled temperatures.
Source: Ersek 2008.
speleothem record in Oregon Caves shows strong correlation with global paleoclimate record
Temperature, precipitation and vegetation are all major
factors affecting the growth of formations in the cave.
Temperature controls the distribution of oxygen isotopes in
rainwater and therefore speleothem, and thus by analyzing
the speleothem record we can examine temperature changes
in the region over time (Ersek 2008).
δ18O as an indicator of temperature change, while the δ13C
is interpreted as reflecting mainly changes in precipitation
and soil biomass. The history of climate changes in the
region for the past 380,000 years is based on data from
speleothems in Oregon Caves is recorded in a dissertation by
Ersek 2008.
The speleothems in Oregon Caves also record global-scale
climatic events. For example there is evidence of a global
cooling ~13000 yrs ago (the Younger Dryas event) in a
stalactite sample taken from the cave in 1930 and analyzed
in 2000 (Vacco 2005).
Most speleothem growth occurs during
interglacial periods.
Note that the Earth has cycled through
about 20 glacial-interglacial periods in the
last 2.5 million years. The most recent
glacial period was 120,000-11500 yrs ago;
we are currently living in an interglacial
period for the past 11500 yrs.
some formations form underwater such as these
rounded limestone ‘cave grapefruit’ stones
Was the cave flooded in the past? Flooding can occur in the Cave. In November of 1974,
flooding began 24 hours after a major rainfall. The water
rose over a foot over the trail in Watson’s Grotto. (Flow
usually increases within about two days after rain begins in
the lower part of the cave.)
During deglaciations, silts and gravels shaped by frost
heaving and meltwater may have raised the level of
surface streams and the water table, and, perhaps due
to glacial ice, Cave outlets to the surface as well as the
deeper Cave passages were blocked.
The resulting floods inside the Cave enlarged side and
upper, drilled domepits into the Cave, and also etched
bevels. Gravels were deposited inside, during initial
entry of surface streams into the Cave and then, as
exits were plugged or partly plugged by the gravels,
slackwater silts were deposited during major floods on
top of the gravels.
There are two separate creeks located
in the Oregon Caves area that could at
one point have been joined at least by
flood overflow. At present, the bigger of
the drainages (Lake Creek) has cut
down below Cave Creek.
Rounder pebbles= longer time being
transported by rivers.
The roundness of pebbles in the
Cavess could be evidence of a longer
stretch of surface stream (as in the
ancestral Creek), and/or lower slope
gradients than that of the current state.
Dating of cave pebbles showed that
uplift caused faster erosion and cave
formation in the Sierras from one to
three million years ago.
cave scallops
Scallops are formed by water flow in
caves. Eddies and swirls locally
present in the water dissolve away a
part of the bedrock and so, they
generally dig an asymmetrical hole, the
scallop. Originally, they were used for
determining paleo flow direction. The
steeper side faces the previous
downstream, and the opposite faces
the upstream. Later, it was learned that
scallops can also indicate the flow
velocity. Thus, the bigger the scallop
is, the slower the water flowed into the
cave: the length of the scallop is
inversely proportional to the flow
velocity. (Though other parameters
such as water viscosity, temperature
and the dimension of the conduit do
play a role.)
Critters in the Cave
Troglomorphic species have evolved
to live in cave habitats
Characterized by features such as loss of
pigment, reduced eyesight or blindness, and
extension of body appendages compared to
surface or soil relatives. A few (springtail,
grylloblattid) may occur in the Caves.
Cave millipede with feeding springtails, Oregon Caves.
The cave at Oregon Caves is home to a
handful (at least 4-8) of endemic species or
subspecies unique to this cave in the world.
a springtail, a type of
hexapod (6 legged but not
an insectt) in the cave
harvestmen
(non-poisonous)
pump up and down
with their bodies
(‘push-ups’) to emit
odor for defense
Since 2012, access in the cave between the Main Entrance
and 110 Exit has been restricted to protect habitat for
hibernating bats during the winter season. ORCA is home
to several migratory or hibernating species of bats that
require isolation.
Although the ORCA hibernating bat population is small in
number, its relative isolation may prove useful in protecting
individuals from contracting White Nose Syndrome should
it spread west of the Rockies. Of the 10 species reported in
Oregon Caves, the Townsend’s Big-earned bat is
designated by the state as a “Sensitive Species,” and