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The recent lava flows from the current eruption from the Kilauea volcano in Hawaii have generated a considerable amount of interest and concern for property.

In the article slow-motion disaster as lava nears main Hawaiian road, USA Today suggests that the variable speed of the lava flow has caused considerable concern and uncertainty:

"It's like slow torture," said Paul Utes, who owns the Black Rock Cafe in Pahoa. "It speeds up, it slows down, it speeds up, it slows down. It's not like any other event where it comes and goes ... and you can move on."

Predicting the future speed of the lava flow simply isn't possible, geologists say, because the advance rate is extremely variable and depends on how much lava the volcano produces.

Despite that evasion, it seems there must be more to the story...
What geological processes affect lava flow speed from the Kilauea volcano?

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    $\begingroup$ I am not convinced USA Today understands the people they're quoting, and am fairly convinced that they're misrepresenting what was said; I'll have a bash at this this evening, though... $\endgroup$ – kaberett Nov 4 '14 at 12:31
  • $\begingroup$ According to my twitter feed it sounds like it has recently had a few breakouts: this reduces the pressure on the main front so it seems to slow down. Of course if you're by a breakout you think the opposite. I think the quote might be referring more to breakouts than lava production (which I agree sounds like a misquote) $\endgroup$ – winwaed Nov 4 '14 at 13:49
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    $\begingroup$ The lava flow speed is only marginally related to the amount of lava produced. The important factors are the lava viscosity (function of silicon content and volatile content) and temperature. You might want to edit your question to get a better answer. $\endgroup$ – Gimelist Nov 4 '14 at 15:52
  • $\begingroup$ @kaberett I have modified the question. $\endgroup$ – user889 Nov 4 '14 at 19:38
  • $\begingroup$ @winwaed that could be a major mechanism, have modified the question. $\endgroup$ – user889 Nov 4 '14 at 19:40
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The speed of the lava flow from Kilauea depends on a few things:

  1. The amount of activity at the source of lava. This flow you are talking about is coming from a vent that is 20 miles from the Kilauea caldera. So, it is more like a leak, than a true eruption. There's not a lot of force behind these types of events and thus not a lot of lava coming out.
  2. The viscosity of the lava. This is basalt, so it can move pretty quick, for lava.
  3. The terrain. The source of the lava is not near the summit, but rather far down the mountain at only 700 ft elevation. The surrounding terrain has a very shallow slope, which doesn't allow the lava to move downhill quickly.
  4. The cooling rate of the lava. It rains a lot in Pahoa. Especially in late October. This helps to cool and harden the lava, which slows the movement.
  5. Barriers and surface characteristics. There are a lot of natural contours in the land, trees, and brush in the Pahoa area. This helps to slow down the movement.

Having grown up on the Big Island, I can say from experience that these flows that come out of side vents are often slow enough to walk right up to and play with. They don't move fast at all. The reason it's such a big news event is because it nearly covered a main highway, which would've cut off a lot of people from the main town, Hilo.

The fast-moving lava flows usually come from the main caldera, where the amount of lava erupting is far greater. Also, Kilauea is really just a pimple on the side of Mauna Loa. So, it is a bit of a release valve for the big volcano. Shouldn't be too long before Mauna Loa erupts again and then you will see a lot of fast moving lava from a 13,000+ ft location.

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