Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS

NOVA Online: Lava Sampler
photo: Michael Garcia 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 easiest volcano.

NOVA: Explain a little about how the lava here flows.

quote: It's very haunting to think that there is a force behind all of this and you're merely a passenger riding along on this grand voyage. 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 the sea.

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 that?

Garcia at the pit 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.
(continue)




Support provided by

For new content
visit the redesigned
NOVA site

return to the Hawaii homepage


NOVA Home | WGBH Home | PBS Home
Search | Feedback | Shop
© 1996 WGBH