[Aztlan] Teotihuacan tunnels and lava formations

[Hayley Smith]

I wanted to clear up a misconception here. Kim Goldsmith wrote:

"The volcanic formation the tunnel is in is NOT a lava TUBE.....it is a lave
TONGUE.  That's how we know it was manmade.  The way Linda's team explained
it is that a lava TUBE is a consistant flow in which bubbles can form, and
once cooled those bubbles become caves.  A lava TONGUE is where "spittage"
from a live volcanoe comes out little by little over hundreds or even
thousands of years, cooling practically in the air and then landing on the
ground as one rock on top of another, with dust and dirt in between the
pile-up.  There is not one single lava TONGUE in the entire world where a
natural cave has been known to form, and Teo. is no exception to this rule.
The removal of rock from this type of formation is extremely easy, and only
for the very largest chunks would you even need a lever.  The normal size of
the rocks that make up the tunnel's "roof" and walls are aprox. the size of
what you see them using in building on the surface at the site."

This information is mostly incorrect. Lava tubes have nothing whatsoever to
do with bubbles in lava flows. Lava tubes are formed when flows of pahoehoe
(hot, smooth, and runny) lava cool and harden. They form walls and ceilings
that insulate the hot lava inside, allowing it to run sometimes for many
more miles. You can see lava tubes forming at the Hawaii Volcanic
Observatory website: http://hvo.wr.usgs.gov/ It is possible to get gas
bubbles inside lava tubes, which can form cupolas and domes, but gas bubbles
on their own do not form lava tubes. Lava tube caves form when the surface
of a lava tube collapses, exposing the area underneath. A cupola made by gas
could open up an entrance to a lava tube, but they do not form caves on
their own.

What Kim is describing as a "lava tongue" is a spatter cone. Here is an
example from Flickr of what a lava tongue actually looks like:
http://www.flickr.com/photos/wildergeek/7186437/ As you can see, it's not
the kind of cooler, less plastic lava that spits up from the earth; it's a
hot, runny lava that oozes out of a flow, forming something that looks like
a toe. You can find lava tongues in many, many places inside and outside of
lava tubes. It is correct that caves cannot form in lava tongues, because,
well, it just doesn't work that way. You could possibly get some kind of
talus cave forming in one, but it could only be a few feet high.

Just wanted to clear that up!

Hayley E Smith
Park Ranger
Lava Beds National Monument
Vanderbilt University

Josh Welter
SCA Intern
Lava Beds National Monument
Clemson University