Las Tres Hermanas (y sus hermanitos)
A
cache
by Grasshoppers&Ant
Hidden:
3/21/2008
Size:
 (Not chosen)
Difficulty: 
Terrain:
(1 is easiest, 5 is hardest)
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Albuquerque’s western horizon is marked by Las Tres Hermanas – The
Three Sisters volcanoes, plus two smaller cones and a few other
volcanic ‘humps.’ From south to north (LtR below) they are JA,
Black, Vulcan, and the little brothers Bond and Butte.
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). |
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
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