This line of unique volcanoes is located on Petroglyph National
Monument, a 7,236 acre (29.28 km2) park created in
1990 to preserve the unique cultural and natural resources
including the volcanic cones, “archaeological sites and an
estimated 25,000 images carved by native peoples and early Spanish
settlers.” [1]
The Petroglyphs were etched on the volcanic rocks, rocks whose
minerals oxidized to form the desert varnish coating on the
surface. However, do not expect to see petroglyphs near the
volcanoes and the trails to the west that lead to them. They are
found on the east slope of the mesa; the western portion of the
park offers “a lesson in the greater volcanic geology and
creation of the National Monument.”[2]
The Rift between us
The Albuquerque volcanoes are a relatively recent addition to the
Rio Grande Rift Valley’s history, their advent being a direct
result of the rift action.
This volcano story began long before the eruptions about 150,000
years ago (some sources estimate 130,000 years ago). Beginning 25
Million years ago the earth’s crust in New Mexico was
“sporadically stretched and thinned between the Colorado
Plateau… to the west and the Great Plains … to the
east.” At the same time (geologically) during the rifting,
the Sandia, Manzanita, Manzano, and Los Pinos Mountains began
uplifting along the east side.[3]
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Map of Rio Grande Rift region
showing rift basins (from USGS).
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Rifting is not a ‘smooth’ process and results in a
series of basins rather than a single long depression. Albuquerque
is in one of these basins and was slowly filled with sediments from
rivers and streams originating to the north and west. The sediments
that filled the basin are known as the Santa Fe Formation. As the
rift deepened, the rivers and streams eventually ran north to south
and finally merged to create the Rio Grande. This formation of the
Rio Grande (river) valley occurred about 1 million years
ago.[3]
Today the rift manifests itself in the Albuquerque area over the 40
miles between the Sandias and the Rio Puerco.
The way was opened
With the spreading crust creating an unstable area subject to
earthquakes, and with the thinned crust in the rift valley, the
stage was set for an eruption! If you were hoping for a big
explosion, unfortunately this was not the case. A five-mile long
deep crack (below the surface) in the crust, or fissure, was likely
opened by an earthquake and magma arose to the surface. As this was
a ”non-violent fissure eruption, lava flowed eastward in a
sheet-like fashion and covered the Santa Fe Formation.” This
was now about 150,000 years ago. The cooled lava is the black
basalt rock you see in the National Monument.[4]
The cooled lava then blocked the fissure except for in a few
places, vents, where “cinder and lava accumulated creating
the volcanic cones we see today.” On the east slope of the
mesa, the basalt rock broke apart leaving tons of materials for the
ancient artists.[4]
Scoria? Spatter?
Although fissure eruptions are not uncommon and can be seen in
Hawaii and Iceland, the fissure that gave us this line of scoria
and spatter cones is unusually long. Scoria cone, or cinder cone
volcanoes are typically steep conical hills. The rock fragments
contain numerous gas bubbles "frozen" into place as magma exploded
into the air and then cooled quickly.[5]
Similarly spatter cones are formed when the erupting lava
contains enough explosive gas to prevent a lava flow, but not
enough to shatter it into small fragments. The lava is torn into
liquid hot clots by expanding gasses called spatter. When the
spatter that has solidified accumulates around a vent it is called
a spatter cone. “A spatter cone is formed of molten lava
ejected from a vent somewhat like taffy. Expanding gases in the
lava fountains tear the liquid rock into irregular gobs that fall
back to earth, forming a heap around the vent. The still partly
liquid rock splashes down and over the sides of the developing
mound is called spatter. Because spatter is not fully solid when it
lands, the individual deposits are very irregular in shape and weld
together as they cool, and in this way particularly differ from
cinder and ash.”[6]
Dr. Larry Crumpler, Curator of Research, Volcanology &
Space Science at the NM Museum of Natural
History and Science, says at this
link that some of the Albuquerque volcanoes, including Vulcan,
were “cones formed from spatter and thin lava flows coating
an interior of cinder.”[7]
To log this EarthCache:
0. If you don't know how an EarthCache is different and
why there is no container here on NPS land, read this and
this.
1. Review the park regulations
page.
2. Hike from the Petroglyph National Monument Day Use
area [Parking/Trailhead waypoint] to the posted coordinates just
north of and below Vulcan’s summit. In your log, post a
photo of yourself and/or your GPSr with one or more of the
volcanoes in the background nearby.
As the Park Service notes, “Ancestral and Modern Pueblo
peoples believe that hiking to the top of the volcanic cones
desecrates this landscape. Please respect this belief by not
climbing on or to the top of the volcanoes.“ Please stay on
established trails as you will not need to hike to a summit to log
this EarthCache. The trail loops around the summit.[8 ]
If you start and return to the trailhead at the NW corner of the
lot, the distance is just over 2 miles round trip. If you loop
around the cone and over Black to the trailhead in the SE corner,
plan closer to 2¾ miles with more elevation changes. If you
park near the outer gate near Paseo del Vulcan, then add an
additional quarter mile each way.
For your hike it is also worth noting that “this area is
fully exposed, with no cover from the elements. Lightning can
strike at anytime so please keep the weather forecast in mind.
Weather can also change within minutes.”[2] Take Drinking Water!
3. On your hike look for evidence of scoria (rock
fragments containing numerous large gas bubbles) and/or
spatter (heaps around the vent or irregular shaped deposits
that may be welded together). Post a photo and description of your
find. I saw (I think) spatter evidence on the south-facing slope
near the top. Can you find any other? Volcanic basalt rocks with a
white-deposit coating are not evidence of either, but caliche, a
calcium carbonate substance which is described on the national
monument website.
4. Bonus Question: Petroglyph NM is 7,236 acres. Suppose
that the lava flows covered 10,000 acres to a depth of 10 feet, and
taking a uniform specific gravity of 3 for the basalt, roughly how
much lava flowed from the fissure? Adding in the volume of the five
cones is trickier without knowing their heights, but you can make
reasonable guesses for those and add them in too if you like.
The placement of this EarthCache was approved by the management
of Petroglyph National Monument. Thank you!
References:
-
Wikipedia, "Petroglyph National
Monument", http://en.wikipedia.org/wiki/Petroglyph_National_Monument
- Pro Trails® "Albuquerque Volcanoes - The
Three Sisters: 2.0 miles", http://www.protrails.com/trail.php?trailID=244"
- Crumpler, L. S., Newsom, J., and Aubele, J.
2004, "Albuquerque's Geoscape": poster, http://www.joannewsom.com/AlbuquerqueGeology/
- National Park Service, "Geology: Designer of
the Land", http://www.nps.gov/petr/planyourvisit/geology.htm
- USGS Volcano Hazards Program, "Photo
glossary of volcano terms: Cinder cone", http://volcanoes.usgs.gov/Products/Pglossary/CinderCone.html
- Wikipedia, "Volcanic cone", http://en.wikipedia.org/wiki/Volcanic_cone
- New Mexico Museum of Natural History and
Science, "The Albuquerque Volcanoes. Frequently Asked Questions",
http://www.nmnaturalhistory.org/volcano/albq_faq.html
- National Park Service, "The Volcanoes",
http://www.nps.gov/petr/planyourvisit/volcanoes.htm
