|Lookout Mountain is widely known for its
many unusual geological features. The most unique of which being Ruby Falls, a 145 foot underground waterfall located over
1120 feet beneath the mountain’s surface. The fascinating story of the formation of Lookout Mountain, the Ruby Falls cave and Ruby Falls itself is told by how the rocks that formed
each of these wonders did so.
Click the links below for each subject
Formation of Ruby
Formation of the Waterfall and Falls Room
Formations in the Cave
Formation of Lookout Mountain
Most of Lookout Mountain is made of limestone rock. About
240 million years ago, a shallow sea covered the eastern
Tennessee area, and it was in this sea that the limestone of
Lookout Mountain was formed.
Limestone is a sedimentary rock formed by successive layers
or shale, sand, and pebbly sand. The layers of sediment
hardened over time to form limestone rock.
Millions of years ago the North American and African plates
collided in a collision that lasted for several thousand
years. The collision was felt even as far inland as the
Chattanooga area. These tectonic forces produced a series of
earthquakes that pushed and bent the hardened rock to form
The bending and folding of the brittle limestone and sandstone layers cased a series of cracks and crevices to form. The rock layers slid past each other along what geologist call faults. These faults were the very beginning of Ruby Falls Cave.
Formation of Ruby Falls Cave
The Ruby Falls cave is located deep in the heart of Lookout
Mountain. It is a limestone cave (sometimes called a
solution cave). The process that forms a limestone cave can
be broken down into a few steps:
1. Carbon dioxide in the air is absorbed by rain water
falling through it. The rain water also absorbs carbon
dioxide that is in the soil after it hits the ground.
2. Water breaks carbon dioxide down into a very weak acid
called carbonic acid.
3. The weak acid comes into contact with limestone rock when
subterranean streams find their way through the cracks in
the limestone rock that have been produced by tectonic
4. The acid solutes (or eats away) the limestone (which is
made of calcium carbonate or calcite) causing the cracks to
become larger and caves and passages to form this process is
called chemical weathering
At one time the water table was much higher and the Ruby
Falls Cave was at the top of it. Rushing water flowed
through for many years washing out the cave and enlarging
the faults and cracks. The water table has since lowered and
that explains the lack of water in the cave.
Formation of the Waterfall and Falls Room
After the formation of the Ruby Falls Cave, a surface stream
entered it and left deposits of sand and gravel along the
walls. It was during this time that a sinkhole developed
near the head of the stream and allowed great amounts of
water to enter. The presence of sand and clay along the
sides of the cave confirm the presence of a sink hole at one
The water hollowed out the dome area that Ruby Falls is
located; this area is sometimes referred to as “Solomon’s
Temple”. By way of erosion the waterfall carved out this
area. The progress of this natural process can be observed
by studying the smooth sides of the limestone walls.
Formations in the Cave
Over the years, the water level in the cave lowered and air
entered the Ruby Falls Cave. When that happened the
conditions were right for the formation of speleothems, or
The formation process takes a very long time. It is a very
simple process though: water moving through the soil absorbs
the minerals in the limestone. As the water evaporates or
drips it leaves minerals behind.
Stalactites form as water
drips from the ceiling leaving minerals behind, the minerals
build up very slowly to make the
stalactites start out as
capillary tubes (also called soda straws.) A capillary tube
is a hollow
They are very thin and fragile. When the hole on the end of
a capillary tube is closed off, it becomes a
stalactite, and begins to
widen. Capillary tubes are very common in the Ruby Falls
Cave especially in the Hall of Dreams.
Stalagmites are formed by
minerals deposited on the floor when the dripping water hits
and leaves behind minerals.
Stalagmites almost always form underneath
Columns are formed when a
stalactite and stalagmite grow into each other.
Drapery formations (also called
curtains) are formed as water works its way through the
small cracks and crevices in the ceiling and evaporates
before it has a chance fall.
Flowstone is formed from
flowing water instead of dripping water. The calcite is
deposited in thin layers. These thin layers will first take
the shape of the cave floor or bedrock underneath it. The
flowstone builds up to
become more rounded as it gets thicker.
Helictites are a type of
in any direction on the cave ceiling. Their twisted shape is
attributed to air currents and the arrangement of the
crystals of calcite.
Caves often provide homes and shelter for a variety of
animals. Since Ruby Falls cave has no natural entrance, we
are unlikely to find critters living here. Generally
speaking cave animals are divided into three categories:
Cave dwellers (troglobites) are those who spend their entire
life in caves (blind cave fish or crawfish).
Cave Guests (troglogenes) are those who use caves for
shelter or hibernation but usually live above ground (bats,
Cave Lovers (troglophiles) are those that live most of their
lives in caves. They are usually found near the entrance
where some light filters in. They move back and forth from
the outside to the inside as they search for food
(salamanders, Cave crickets).
Calcite: A mineral, calcium carbonate (CaCO3); the major
component of limestone and nearly all formations.
Capillary Tubes: The first stage of growth of a stalactite,
a narrow fragile formation that is hollow.
Cave: A natural underground chamber or series of chambers
usually open to the surface.
Chemical weathering: A process which breaks down rocks by
the action of chemicals.
Column: A pillar-like structure formed when a stalactite and
a stalagmite have met and joined together.
Curtain: A thin, translucent sheet of calcite formed when
water flows down the inclined ceiling of a cave. (Drapery)
Erosion: the process by which weathered materials are
carried away by wind, water, or glaciers.
Fault: A crack or parting in a rock, often occurring in sets
or parallel groups.
Flowstone: A surface coating
or a calcite layer that has been deposited by a descending
film of mineral-charged cave water.
Helictite: A distorted and twisting stalactite that grows
with a seeming disregard of the pull of gravity.
Limestone: A sedimentary rock composed chiefly of the
mineral calcite. It is easily dissolved by acidic ground
water, most of the world’s caves are formed in limestone.