Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Daniel Spooner
Caves and the Treasures They Hold.
Caves or caverns as they are sometimes called come in many shapes sizes and forms, the 5 most common being, Solutional, primary, sea, fracture, and glacier. Recently confirmed however, are caves formed by sulfuric acid, this is significant because a cave formed by sulfuric acid is created from the bottom up, rather than from the top down. Defined as a naturally occurring subterranean void, caves are found all over the world and few people realize just how many economical purposes caves serve. Examples of the services caves provide include: organic fertilizer, birdsí nests, medicinal compounds, and varied aesthetic mineral formations.
Types of caves
The most common type of caves, Solutional caves,
form by carbonic acid dissolution. When rain falls to the earth, minute
quantities of carbon dioxide combine with the water creating a slow acting but
powerful acid known as carbonic acid (carbonated water). When carbonic acid
seeps into the ground, it acts as any liquid does following the path of least
resistance, most commonly cracks. Once the acid is in a rocks natural crack, it
begins to dissolve the surrounding rock, eventually leaving behind a cavity.
(Deer cave, Mulu National Park)
Primary caves are caves formed
at the same time as the rock surrounding it. The most common and well known are
lava tubes. Lava tubes are formed when lava flowing down a hill solidifies on
the surface while staying liquid underneath. Then, the lava drains out as no
more lava travels down this channel, leaving behind a round tunnel.
Sea caves, or littoral caves as they are sometimes called, are caves formed by
the pounding of the oceans waves. When waves hit a cliff, the constant pounding
of the water and whatever else picked up by the waves slowly erodes the base
away. But, when waves hit a cliff with faults, dykes, or bedding plane contacts
(where layers of soil converge), the weakened cliff side is rapidly eroded away
creating a cavity.
Fracture caves are
formed when layers of water soluble rock, such as gypsum, halite (salt), and
sylvite, come into contact with water. Once these rocks are dissolved, they are
carried away leaving a cavity behind. This differs from Solutional caves in
that it is water which creates a cavity, rather than carbonic acid.
Glacier caves are formed when a
large block of ice (a glacier in most instances), slowly begins to melt. As
the ice melts, it creates a channel in which to flow. As more and more ice
melts it enlarges the cavity sometimes to massive proportions. However, as it
is made of ice, glacier caves are very short lived and subject to sudden
collapse and re-freezing.
Caves form by sulfuric acid, when hydrogen sulfide leaks over from adjacent oil
deposits dissolving limestone and depositing gypsum. The best known example of
this is Lechuguilla cave in Carlsbad New Mexico. The acid rises from below as a
gas, dissolving rock and creating a cavern from the bottom up, while depositing
spectacular gypsum formations.
Economical products of caves
Living in many caves with wide
openings above ground, cave swallows are a common cave sight. When it is time
for cave swallows to lay their eggs, they will use their saliva to construct a
bowl shaped nest. When swallows nest however, hundreds of people climb to the
top of ladders (or even just a rope) to collect these delicacies, turning them
into birds nest soup (common delicacy eaten in China). This is very dangerous,
for the nests are always made at ceiling level, sometimes over a hundred feet
up, with many people dying each year.
Another common commodity
collected in caves is guano (bat excrement). When a large colony of bats live
in a cave, (bat colonies can number in the millions) large quantities of guano
builds up below. Being very high in phosphorus and nitrogen, guano is harvested
every year for use in fertilizers and gunpowder. Yearly, thousands of pounds of
bat guano are mined out of caves, packaged, and shipped all over the world.
Guano is so valuable in fact, that in 1879 a war broke out over guano harvesting
Over the course of the past
decade, scientists have been studying micro organisms called Chemolithoautotroph
found only in caves formed by sulfuric acid. These micro organisms are believed
to have medicinal qualities beneficial to humans and are being experimented
with. Unfortunately, the results of their research have not been published.
(Couldnít find any pictures)
Of all the commodities found in caves however, nothing could compare to the
beauty of mineral formations. Forming in diverse ways, there are many types of
mineral formations. The most common of them are: stalactites, stalagmites, soda
straws, flow stone, cave pearls columns and helictites.