Volcano Watch — Lava expected to flow over pali toward Kamoamoa soon

The episode 51 vents adjacent to Pu`u `O`o on the East Rift Zone of Kīlauea Volcano have been in continuous eruption since before dawn on June 21. Until this period, episode 51 has been characterized by off-and-on activity since it began on March 7. The current eruptive interval is by far the longest and most stable since that time.

Since February 17, a low lava shield, surmounted by a perched lava pond, has formed just uprift from Pu`u `O`o. However, flows from the episode 51 vents had been confined to the flanks of this new shield until this past week. The pahoehoe flows have now advanced to the south off of older flows produced during the Pu`u `O`o high-fountain episodes and during episodes 50 and 51. On Thursday afternoon, the flows had advanced more than two miles from the vents, to about the 1,950-foot elevation and were burning through the forest as they approached the pali about halfway between the two westernmost `a`a flows erupted from Pu`u `O`o.

If the eruption continues unabated, the flows should reach the pali this weekend and begin to flow more rapidly down the steeper slope. At the base of the pali, above Kamoamoa, the slope flattens and the flows will tend to spread out rather than continue to advance rapidly to the sea. The flows should be visible from Chain of Craters Road near Kamoamoa, inside Hawai`i Volcanoes National Park, if they reach the pali. There are no homes or other structures threatened by this flow, although several important archaeological sites could be inundated by lava.

For the past two weeks, lava has not passed through the perched pond on the growing shield but has flowed directly from the active vents through tubes. There is no sign of active lava on the new shield or at the spatter cones formed earlier in the episode 51 eruption. The first place where lava is visible on the surface is at the southern base of the shield. The long duration of this eruptive interval has allowed efficient tubes to form beyond the base of the shield. These tubes feed lava to the advancing flows downslope.

The lava lake inside Pu`u `O`o remains active at a depth of about 215-230 feet below the rim of the cone. This lava lake produces a bright flow at night and a heavy plume of fume that can be seen from Highway 11, or from the lookout atop Pu`u Huluhulu on the Napau Trail in Hawai`i National Park.

The new episode 51 shield has followed a development similar to that observed in 1986 when the Kupaianaha shield first formed. Both were characterized by a period of shield growth with no flows advancing far beyond the base of the shield, both developed a perched pond and tube system that delivered lava to the base of the shield, and both ponds crusted over so that lava was no longer visible near the vents. The main difference has been the time it has taken to reach each stage.

At Kupaianaha, the perched pond developed rapidly, whereas the episode 51 pond did not develop until several weeks into the eruption. The Kupaianaha shield created a tube system that delivered lava all the way to the ocean in less than five months, whereas the episode 51 flows have barely extended off the shield in six months. The pond at the summit of Kupaianaha did not empty until after nearly four years of eruption, whereas the episode 51 pond has emptied in less than six months. Each of these differences is probably related to the rate of lava production, with the rate during the formation of the Kupaianaha shield far greater than that during episode 51.

This decrease in the rate of lava production seen at the vents and the general decrease in the amount of sulfur dioxide gas emitted through the summit of Kīlauea Volcano indicate that the supply of magma feeding the eruption is dwindling and that the eruption is slowly dying. It is more difficult to forecast when the entire eruption may end. However, we still forecast that, before the eruption is over, eruptive activity may migrate uprift, toward the summit, and even to the summit caldera. Such events would more clearly indicate that the end is near.