Hotspots Calderas and All That
(Excerpt from: How do
we know? Available on Amazon.com:
by
Kenny A. Chaffin
All Rights Reserved © 2013 Kenny A. Chaffin
Yellowstone is well past due for a
massive eruption. The magma chamber 6 miles beneath it is growing larger and
faster than at any time in human history. We know that Yellowstone erupts every
600,000 years or so and the last eruption was 642,000 years ago. Now while past
performance does not guarantee future events, we are past due for this one. Past
eruptions occurred 2 mya (million years ago) and 1.3 mya as well. These were
massive eruptions 1000-2000 times that of the Mt St. Helens eruption of 1980.
This image shows the
basic geology of the Yellowstone area and caldera. This area and others like it
around the world are caused by mantle plumes.
By
examining and mapping the terrain of the area each of a few recent eruptions
can be seen in the separate calderas they left. These are indicated in this image
from the U.S. National Park Service.
The three
most recent eruptions (2.1, 1.6, and .6 mya) are all in the current Yellowstone
area as shown in the previous caldera image. The following image shows the movement
of the hotspot back some 16 million years into Oregon and Nevada. It is a bit
deceiving but it’s not the hotspot that is moving, it is the crust of the Earth
moving above and across it. The hotspot rises up from the magma layer below and
the North American continental plate moves from North/East to South/West above
the hotspot as the continent makes its way steadily and irrepressibly towards
the Pacific subduction zone under California. This makes it appear as though
the hotspot is moving to the east/northeast but it is actually the continent moving
over the hotspot.
Each past eruption
has been unique with varying impacts on the geography, fauna and flora. We can
see this by examining the geological evidence in the ash it expelled in amount
and extent as well as the evidence of pyroclastic and lava flows. The smaller
eruptions seem to have devastated life in the four surrounding states – Idaho,
Wyoming, Colorado and Nebraska. The larger eruptions devastated the entire
western half of the United States from Canada to Mexico and from the Pacific Ocean
to the Mississippi River.
Scientists are constantly watching,
measuring and monitoring any movement, tremors, geological or volcanic activity
in the area. From 2004 – 2007 the floor
of the Yellowstone caldera rose about 3 inches each year. This is three times more than in prior years.
The rise is attributed to the growing magma bubble under the region which is
slowly pushing the crust upwards. It has slowed slightly since 2007 but continues.
Yellowstone
and other areas like it, past and present are due to these so-called hotspots
on the Earth’s crust. If look at the interior of the Earth we know there is an
inner core of solid iron that is under extreme pressure and is extremely hot.
The temperature is well beyond the temperature of liquid iron but remains solid
due to the pressure at that depth. A brief aside on this, scientists recently
discovered that the Earth’s inner core is actually 1000 degrees hotter than had
been previously thought which solves a long standing problem involving the
Earth’s magnetic field. The lower temperature would seem to make the magnetic
field impossible so there has been much consternation over it. How did they
determine this? You can refer to the article in the reference section, but
basically by using x-rays, particle accelerators, lasers, diamonds, and iron
for measuring and simulating the conditions. It is now thought that the inner
core is 6000 degrees Celsius -- hotter than the Sun.
This solid inner core is surrounded
by a liquid iron which is in turn surrounded by molten magma that swirls and
circulates in an extremely slow rolling boil like candy or fudge on your
kitchen stove. All this heat and pent-up energy sits beneath the thin
egg-shell-like crust on which we live. That energy sometimes escapes through
areas such as Yellowstone, volcanos like Mount Saint Helens, Etna, or those with
the unpronounceable names in Iceland. The rolling boil of the magma is what
drives continental drift, pushing up new crust at the mid-ocean ridges and
pulling old crust down into subduction zones over the millennia.
Hotspots such as Yellowstone are
areas where the crust is thinner than average due to the molten mantle pushing
upwards warming it and creating volcanism, hot springs, sulfuric and other volcanic
gas emissions. In addition to Yellowstone, it is a hotspot that is responsible
for the Hawaiian Islands as well as some forty other areas around the world. Throughout
history these hotspots have resulted in some of the most deadly events
imaginable.
The Deccan
Traps in west central India began erupting approximately 65 million years ago
contemporaneously with the extinction of the dinosaurs and was likely at least
partially responsible for their demise. As with Yellowstone and other past
‘trap’ events it was due to a deep mantle magma plume erupting onto the surface
of the Earth. The word ‘trap’ comes from the Dutch word for stairs because
these types of lava flows result in a stair-stepped appearance as repeated
flows build up atop one another. The Deccan Trap event may have caused cooling
of the Earth by two degrees Centigrade due to release of sulfur dioxide and
other volcanic gasses but it is not thought to have been the primary death
dealer to the dinosaurs. That title goes to the Chicxulub impact event in
Central America. An asteroid 10 km in diameter struck the northern Yucatan
Peninsula area which blanked the Earth in a deadly dust cloud cutting off the
sunlight, killing most plant life and ultimately the dinosaurs as well. The Deccan
eruptions lasted 30,000 years and certainly contributed to that deadly atmospheric
blanket. They exuded enough molten magma to cover 1.5 million kilometers about
half of the modern India.
Deccan Traps area
(Photo of Rajgad Fort taken from Pabe Ghat.)
A still bigger event was the
Siberian Traps event of 251 mya. It is thought to have been responsible for The
Great Dying which killed 96% of all marine species and 70% of all land species
including insects. Some 57% of all families and 83% of all genera
became extinct. This is also called the P-T Permian–Triassic extinction event
and while we can’t say for sure the Siberian Traps event was responsible, it
was certainly the largest part of it. There may have been asteroid impacts (Wilkes
Crater in Antarctica) or other triggers. In any case it took 30 million years
for land-based life to recover. This was a mantle plume event like the Deccan
event but lasted a full million years from 251 – 250 mya. It covered an area of
2 million square kilometers and released from 1 – 4 million cubic kilometers of
lava. This is an incredible volume of molten rock! Even at the minimum of 1
million cubic kilometers this amount of material – assuming it were possible, could
be used to build a 22 lane interstate ‘highway’ 266 feet wide (as well as deep)
between the Earth and the Sun.
Siberian
Traps Area - Physical map of Siberia with extent of Siberian traps
according to http://www.mantleplumes.org/Siberia.html (links provided in lieu of copyright-restricted
image)
The fact
that humanity has not seen an event such as these just goes to emphasize once
more the fleeting amount of experience and time we have existed on this small
planet with our miniscule collection of recorded history. We are so much less
than important, a minor species on a minor planet of a minor sun in an
unconcerned unrelenting uncaring universe. We may be headed towards a sixth
great extinction of our own making but even if we as a species avoid, live
through, or prevent it, we have no control whatsoever over massive eruptions
such as these and depending on the size and extent there would be little we
could do to survive. This is perhaps one more reason to be pushing for
development of space capabilities sooner rather than later. There is little to
be gained from worrying though, we can only hope to survive and we certainly are
survivors we survived the much smaller Toba event some 6000 years ago even if
it was a few thousand of us, we may survive again. There may be some warning,
we are monitoring closely…or there may not, humanity has yet to experience a
true massive eruption, asteroid or other extinction event. Let’s hope we never
do, or that we are long gone from the planet should it happen.
References/Resources/Links
Yellowstone Caldera Image:
Yellowstone Hotspot Movement Image:
Yellowstone Hotspot:
Increasing Magma Inflation under Yellowstone:
Siberian Traps and P-T Extinction Event:
Deccan Traps:
Emeishan Traps:
Hotspot Geology:
The Great Dying, P-T extinction event:
Mantle Plumes Organization:
Earth’s Core Hotter than previously thought:
Rescue Party – Arthur C. Clarke (fiction):
About the Author
