Formation of the Caves
Located about 20 miles southeast of Cave Junction in Josephine County is the Oregon Caves.
Although the name is plural it’s actually just one cave
that stretches 1600 feet long. It was first discovered in
1874 by a deer hunter.1 If you read my home page, you
already know why I chose the Oregon Caves for my
course project. I used to love going there as a kid. I
remember going almost every year for school field trips
and it’s also something my parents used to take me to do. It was a routine, first the Oregon Caves
and then pizza from Wild River Pizza. Anyone who has not been will never fully understand the
beauty of these caves. It’s definitely a highlight for education. So how are we able to enjoy these
majestic caves, In other words where did they come from?
Well according to the National Park Service these caves began forming 220 million years
ago, during the Triassic period. An ocean basin covered the area and was destroyed by the
continental and oceanic rick, leaving animals including bears, lion-like cats, and wolves, living
there until they died1. Their remains hardened into Limestone and solidified as Chert. Then
rocks began folding and uplifting (mountains began to form) because of the pressure from the
earths crust. The limestone began to heat up and transformed from Limestone to Marble, also
know as tectonic activity. The new marble began fracturing and continuing fracturing for a long
time (the exact time frame is unknown according to my research). After the fracturing the
mountains began to process through erosion leaving the area near sea-level2. The overarching
term for the formation of the Oregon Caves is Speleogenesis and thus, we have the Oregon
Caves! And this is what they formed into:
Sounds easy enough, right? Well if you’re like me and this is your first real science class
since high school, that doesn’t make a lot of sense. So let’s break it down. Thanks to the National
Park Service we have these very handy diagrams to help us through it. The first diagram is
showing the beginning of the process, which started 220 million years ago, give or take a couple
years. It shows the original ocean basin being pulled apart by the continental and oceanic rock.
The second diagram is showing the formation of the marble mountains aka the Siskiyous and
also shows the different rocks that are there. Gray is Basalt, Pink is the quartz diorite, and the
white is the marble3.
Speleothems
Speleothems are mineral deposits formed from
groundwater within underground caverns. Also known
as formations, these deposits can’t form until there is an
opening in the cave. There are two different processes
that create Speleothems. The first process involves
evaporating the water and leaving behind the minerals.
This first process is the reason that there must be an opening for Speleothems to form. It mainly
happens near the front of the caves and if you’ve ever been on an Oregon Cave tour you know it
as cave popcorn. The second process is when the water that comes through the caves loses
Carbon Dioxide. When the water originally enters the rocks, it’s under a lot of pressure, but after
it’s entered the pressure is reduced and that’s how the Carbon Dioxide is released (More details
in the photo below). This causes the water to be saturated in Calcite and is the slower of the two
processes but still the most common4. I think what’s more interesting is that Speleothems are a
way to tell what kind of climate conditions existed in the past5. Kind of like the rings on a tree
tell you how old a tree is.
Other popular formations
include Columns, Stalactites,
Stalagmites, Cave popcorn,
Rimstone dams, flowstone, cave
ghosts, boxwork, and Moonmilk.
Not Your Average Limestone Cave
A cave cannot form without a large amount of Limestone. The Oregon Caves are formed
by marble, which is a recrystallized form of Limestone. This recrystallized Limestone was
initiated along with cracks and joints until the pockets were formed and turned into what you see
today which is different “rooms” or caverns.
The water level that had once filled the caverns varied depending on the stream. When
streams deepened, the water level
was lower causing the caverns to
drain. It’s found that the water did
slightly affect the patterns in the
cave. The areas containing water
can be split into two zones. The
upper zone, also known as aeration,
are rocks that are cracked because
they were filled with air most of the time. The lower zone, also know as phreatic, also contains
the same rocks but instead the cracks are filled with water2.
These different zones help us understand the different cave formations because most
caves have a two-step process in each of these zones. The first step is excavation, which is when
the rocks lie beneath the water table. The second step happens when the water table is lower
which allows air to enter and brings mineral matter to the rooms and galleries. This is also
relevant to speleothems and helps with the understanding of the process in which Carbon
Dioxide leaves water2.
But let’s get back to the marble cave idea, I mean it’s pretty cool that only 3 caves in the
United States are made of marble and one of them is here in Oregon (and the only one located in
Oregon). Besides Limestone and Marble, igneous and sedimentary rocks are also found inside
and outside the cave. The picture below is of rocks found in the Oregon Caves. There many
different types of rock found here, but according to the National Park Service the top 6 in the
world are found in the Oregon Caves and a myriad of Calcite formations decorate the cave3.
Because of the minerals and marble in the caves it makes the Cave very fragile. While in
the cave they ask you not to touch the stalagmites, columns, etc. because they could break due to
the oils in human skin. But due to the amount of people that go in and out, small pieces of those
people are left
behind, including
clothes, hair, etc. This
is dangerous to the
Caves. According to
staff at the Oregon
Caves,
“Approximately
50,000 visitors to the
cave a year leave behind tiny bits of clothing fiber, hair and trash. Over time, lint builds up and
can disturb the cave ecosystem.”
References
1Textbook,
page 131
2http://archive.org/stream/oregoncavesnatio00evan/oregoncavesnatio00evan_djvu.txt
3http://www2.nature.nps.gov/geology/parks/orca/
4http://www.nps.gov/orca/naturescience/speleothems.htm
5http://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/speleothem