Kilauea snuck a
Round 6 past us and it's over!
Since I read up a bit on this area for the Decade Volcanoes eBook (Mauna Loa, chapter draft
here), I'll take a stab at explaining this weird behavior. (
Sources in blog links/available on request.)
<Layperson speculation>A little geography: Kilauea is the youngest Hawaiian volcano above sea level and it sits on Mauna Loa's flank.
Mauna Loa might be transitioning into old age, say the boffins, to be replaced eventually by a humungous Kilauea just as enormous Mauna Loa replaced earlier giants that slowly trundled away from the hotspot while riding the Pacific Ocean tectonic plate. This is such a long-term process, though, that it probably doesn't matter to Kilauea's current eruption dynamics.
There is a baby in this family -- a
submarine volcano offshore, a little closer to the hotspot, that still has a thousand feet or more to grow before it rises above the waves, and it's active, too.
In between that seamount and Kilauea, onshore, is a center of seismic activity at
Pahala. Why? The experts are still working on it.
Plumbing: Lava apparently is not scarce here, but it must be pressurized (and gassy) to erupt. The fountaining shows that gas is no problem. Pressure seems to be the issue.
This layperson's understanding is that the plumbing systems of Kilauea and Mauna Loa are separate but influence each other through stress gradients. These are HUGE volcanoes, and at least in part they're riding on an active
fault that also acts as a backstop; all that weight as well as the movement of magmatic fluids, etc., in various cracks and sills (especially against a backstop) must make for very complex and changing stresses all around.
That could be playing a big role in the intermittent fountaining at Kilauea. Also, scientists aren't sure exactly what's going on at Pahala, AFAIK, although it is probably due in part to a magma body, but whatever it is probably is a contributing factor underground, too.
Finally, not only did Kilauea's summit caldera collapse only six years ago (not even a blink in geologic time) but also Mauna Loa is still in recovery from its recent eruption and so is inflating slowly, too.
In addition to complex interactions hidden from the boffins by miles of rock, many "faucets" are open, reducing pressure in the plumbing system. And only so much magma is available from the reservoirs at any given time because resupply from the mantle operates at geologic-time speed.
Geesh -- with all that going on, it probably would be surprising if Kilauea
did have a stable, long-lived eruption right now! </Layperson speculation>