Volcanism and Orogeny
Above left: Mauna Loa, Hawaii, center and right are stratovolcanoes of the
Alaskan Aleutian Islands. Below is the emptying of the Pu u o'o lava lake of
Kiluaea, Hawaii into a lava tube. I hope these pictures are enough to grab your
attention and encourage you to read on :)
In 1987, I received a gift from my parents ... a trip to Hawaii to visit my
uncle. My uncle, Bill Albrecht, lived at the time on the big island of Hawaii
in a little town called Pahala. As a career mechanical engineer, Bill was gifted
with a creative mind, and because he never received a formal college education,
his mind was unfettered with requisite ideas of how things should get done.
His creativity was noticed by the United State Geological Survey team at the
Hawaii Volcanoes Observatory atop Kiluaea. This volcano is the most active volcano
in the world, erupting almost continuously since 1982. Bill designed instruments
that measured the rate of mountain inflation as magma rose from the interior
of the mantle and prepared to vent out onto the surface. While Kiluaea was erupting
in the 1980's, a large cinder cone was built and named Pu u o'o. When the outlet
plugged, Pu u o'o cracked open at its flank and lava poured forth toward the
east coast of Hawaii. Eventually, a lake of lava formed at the base of the new
Kiluaea volcano. That summer, I had the privilege of standing at the edge of
that lava lake and watch it pour into a vent toward the ocean. I sampled red
hot lava with the USGS members. Later, I camped at night at oceanside while
lava flowed underneath the hardened layer of my campsite into the ocean. To
see glowing orange lava in the dark, spattering and exploding as the hot rock
met the cold ocean was an experience I will never forget. That summer sparked
an interest in volcanoes almost equal to my interest in the stars. To better
understand the process of volcanism, and to see what active volcanoes can do,
go to the Kilauea website and surf through those pages.
The pictures found below are all from the Hawaii Island Kiluaea Volcano. While
I have identical photos at my home, I have not yet bothered to scan those images
into the website, so these photos are borrowed from the USGS Volcano website.
Left image is A'a lava, middle photo is a lava flow whose surface will harden
and form a lava tube, right photo is Pahoehoe lava. The difference in the forms
of lava ... all venting from the same magma chamber, is due to different gas
contents. In all three images, as well as those below, the temperature of the
lava was 1200oC. What proved exciting was walking on older lava fields. The
surface is crinkly and full of golden strands of windblown lava called Pele's
Hair. Walking carelessly along, looking for fissures in the lava, I crashed
through the surface layer into small lava tubes. The tubes were long since empty,
but the hollowness remained. When I visited a 20 foot diameter lava tube later
on one of my trips, I realized how scary it is to walk on these dried lava plains,
for I had no idea where the next tunnel might be.
Left image is spatter cone on a flank of the Pu u o'o volcano, middle photo
is the lava lake at the base of the Pu u o'o flank where I stood in 1987, right
photo is one of several dozen eruption fountains from Pu u o'o. The fountaining
of lava reached a height of 2000 feet, and took place like clockwork every 22
days for several years before the hole finally plugged. The lava lake rose and
fell as lava entered a tube system toward the ocean. When the tube became blocked,
the lake would fill and overrun its edges, then spilling over the hillside down
toward small villages below. What was so cool to watch was the interaction of
the dried lava surfaces, being churned by the molten lava underneath. The middle
picture shows the cracking of these slabs. It was like watching fast-play movies
of global plate tectonics. Lava slabs would crack, spread apart, and be subducted
into the molten lake for re-melting To learn more about some interesting volcanoes,
try visiting the Hawaii Volcanoes, Alaska
Volcanoes, Cascade Volcanoes, and
Yellowstone Volcano websites.
Any process which causes mountains to form is termed Orogeny ... whether
volcanic or not.
Giant mountains like the Himalayas
are formed when two continental plates collide and push their material high
into the sky, as seen in the image to your left. These mountains are not volcanic,
do not erupt, and their rock is often a combination of ancient igneous, sedimentary,
and metamorphic rocks.
The images below depict the processes which gave rise to the Appalachian Mountains
of America (below left) and to the Canadian Rockies (lower right). I do not
even begin to propose to teach here the details of mountain formation, but only
to introduce you to the interesting pictures that depict the process.
image to your left is of the eruption of Mt St Helens in Washington. The images
below depict the process of volcano building. The right image is a generalized
view of the subduction of perhaps the Nazca Plate underneath the South American
Plate. The resultant volcanoes are stratovolcanoes with typical pyroclastic
eruptions. This process is responsible for the building of the Cascade Mountains
in Washington. While extremely beautiful to look at, Mt. Hood, Mt. Olympus,
and Mt. Ranier are all active volcanoes. Mt St Helens erupted in fantastic and
deadly fashion in 1980. While the mountain has calmed down, other Cascade mountains
are busy inside their pretty exteriors. In fact, the upper portions of Mt. Ranier
are actually heating up internally. Imagine your displeasure to be eating dinner
atop the Space Needle in Seattle. You are enjoying your fresh fish of the day,
looking northward at Vancouver unaware of the disaster happening behind you.
As the restaurant turns, you suddenly slump in your chair in dread as you see
the rising plume of ejecta from a major eruption of Mt. Ranier. You merely sit
and wait for the shock wave to knock the Needle over. Scary.
Ranier, as it appears during a windy sunset. If you are ever looking to see
a lot of snow ... get on up to this mountain. I was visiting in March, 1999
and the snow depth at the 5000 ft. level was over 30 feet. The road had been
carved by plows to get to the visitor center. There are places on this mountain
which receive over 1000 inches of snow each year.
Volcanoes can be found all around the globe, as this image depicts. Anywhere
were plates subduct, volcanoes will form. If you are afraid of a potential eruption,
then do not choose to live along those plate boundaries.
Volcanoes do not only form at the boundaries of plate. Some volcanoes just
jump out of the ground in the middle of a plate. Please
to move forward to learn about Hotspot
Volcanoes, or return to Earth Introduction.
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