Excerpted Interview with
Michael Garcia, Geologist at the University of Hawaii:
NOVA: How dangerous is it to do lava sampling?
GARCIA: I don't consider sampling to be dangerous. We take the time to look
over the situation before we sample and try and judge whether or not we can
sample, without risk. Occasionally we do get a little bit of a burn here and
there, but in general I think it's very safe. No one's been hurt out here
sampling during this portion of the eruption. Earlier on a man was burned
working with another guy when he turned around and he stepped into lava, but in
general this (Kilauea) is the best volcano in the world to work on—it's the
NOVA: Explain a little about how the lava here flows.
GARCIA: Most people when they think of volcanic eruption think of surface
flows, lava spreading out and winding their way, as a river, down the hillside,
but this particular eruption has worked its way into an underground system of
rivers that move the lava from its vent all the way down to the ocean where it
eventually erupts at the surface. So the lava has actually eaten its way down
to the underlying rock by the intense heat as well as the abrasion of the
moving lava. It's cut for itself an underground cavern through which the lava
is able to flow insulated by the overlying lava from the outside, so it stays
very hot as it moves down the hillside, meandering much like a river until it
eventually reaches the ocean and dumps out and makes the new coastline along
NOVA: Where does the lava come from?
GARCIA: Where does the Hawaiian lava come from? We think the lava is related
to a hot spot deep within the mantle, perhaps a hundred, a hundred fifty
kilometers in depth. There it is melted and rises to the surface in a conduit
underneath the summit of Kilauea volcano. It then is stored in a summit
reservoir and then is shunted through a series of passageways into a rift zone
and it comes down to about twenty kilometers. It rises to within a few tens of
meters of the surface and then passes through (an) underground lava tube system
(set up for research) which is perhaps ten to fifteen feet below the surface
and then eventually works its way down to the coast.
NOVA: How do you measure the temperature of lava?
GARCIA: We use a thermocouple to measure the temperature of the lava. When we
have surface flows we are able to measure the temperatures and the hottest
temperature we have measured is about eleven hundred and fifty-five degrees
centigrade. That is lava that has cooled as a result of fountaining and has
flowed back, fell back onto the ground and cooled significantly, so we think
it's probably closer to twelve hundred degrees when it was underground before
it rose to the surface.
NOVA: When you collect the different samples what information can you get from
GARCIA: One of the things we are still trying to understand is what happens to
lava at the surface, as it flows either through the tube system or across the
surface, one of the things we've noticed is that the minerals within the lava,
in this case there is a green mineral called olivine, seems to be concentrated
within the flow as it goes down the hillside. So as you collect samples at
different locations down the hillside, you see a change in the mineralogy which
also results in a change in the chemistry. So we can study processes and
mechanical segregation within the lava as it moves down the hillside.
Engineers have found as you move a slurry of material, a mixture of water and
rock, that the rock component is concentrated in the faster part of the flow,
whereas the fluid is along the margins and here at Kilauea the same thing
happens, the solids within it, the minerals are concentrated in the faster part
of the flow and is moved down through the tunnel system, tube system, whereas
the fluid part tends to congeal on the sides, and is left behind, so as the
magma moves its way through the tube system, it becomes more and more
concentrated into solids and crystals, as it moves towards the coast.