As lava once again wends its way downslope toward populated areas of lower Puna, we are reminded of the stop-and-start advancement of flows into the Kalapana community in 1990, when it took 10 months of often agonizingly slow activity to cover the Kalapana area with an average thickness of 10 m (33 ft) of lava and destroy more than 100 residences.
As lava once again wends its way downslope toward populated areas of lower Puna, we are reminded of the stop-and-start advancement of flows into the Kalapana community in 1990, when it took 10 months of often agonizingly slow activity to cover the Kalapana area with an average thickness of 10 m (33 ft) of lava and destroy more than 100 residences.
The destruction of Kalapana actually started in late 1986, when a disruption in the tube carrying lava from the East Rift Zone south to the coast redirected lava toward Kalapana. Eighteen homes burned before lava was again redirected to the west.
HVO started voicing serious concern for the Kalapana community after an eruption pause in February 1990.
By the time the eruption resumed, parts of the previous, long-lived lava tube had collapsed. Lava spilled out of the blocked tube system and flowed along the east side of the flow field toward Kalapana. By the end of February, this flow was only 500 m (550 yd) from the nearest homes.
It took more than a month for flows to advance to those homes, destroying two of them April 4. The eruption paused the very same day. In a pattern that was to be repeated more than 10 times in 1990, lava reoccupied the tube system near the vent, but broke out downslope.
The new flows followed the eastern edge of flow field and once again advanced into the Kalapana community. Between mid-April and the next pause in early May, lava covered most of the Kalapana Gardens subdivision, destroying 60 homes, enclosed Kalapana Village in a kipuka, and briefly entered the ocean at Harry K. Brown Park.
The pattern of pauses and renewed flows that destroyed homes and beloved areas continued all summer. In the fall, lava filled Kaimu Bay and claimed homes in Kalapana Shores. For the rest of the year, lava mostly covered previous flows. A residence that burned Jan. 9, 1991, was the last to be taken, at least for the next 19 years.
Lava returned to the area in 2010 and destroyed three homes, two of which were built on the 1990 flows.
Several factors contributed to the lava’s slow progression and spread into a wide flow field through Kalapana in 1990.
First, the terrain was very flat — the average slope was less than 2 degrees, only slightly lower than the average slope in the vicinity of Pahoa. On such low slopes, intervals of advance, in which the flow front thins and the crust cools and thickens, are followed by periods of no advance as the flow inflates behind the front. Eventually, the crust at the front and/or margins ruptures and new lobes and breakouts emerge to start the advance again. Breakouts from behind the front widen the flow field.
Probably the greatest factor, however, was the frequency of interruptions in supply to the flow.
Often, lava is not able to reoccupy the full length of the lava tube after an interruption and breaks out far upslope from the previous front, covering new ground as it finds the new steepest descent path downhill. This is the process we just experienced with the June 27 flow, as lava reoccupied the tube near the vent but broke out downslope, creating a flow that is advancing over new ground toward the Pahoa Marketplace.
The June 27 flow, with its front at more than 20 km (12 mi) from the vent, already is far longer than any that encroached upon Kalapana; indeed, it is the longest flow that has formed during the nearly 32 years of this eruption. This is significant because, even though lava flowing through tubes is well-insulated, it still loses heat as it travels, and lower temperature lava is stickier, making it harder to flow.
This flow is not the longest that we know of on Kilauea, however — that honor belongs to the ‘Aila‘au eruption, which sent flows more than 65 km (40 mi) from vents near the summit about 600 years ago. That eruption probably lasted about 50 years and covered much of the northeast flank of the volcano.
Understanding the factors at play and the time scale of the inundation of Kalapana, both in 1990 and on the longer time scale of impact from 1986-2010, as well as the even longer time scale of eruptions such as ‘Aila‘au, could help us understand the range of possibilities for the unfolding of the current situation.
Kilauea activity update
The lava flow from Pu‘u ‘O‘o that began June 27 remains active and is advancing across state land east of the Wao Kele O Puna Forest Reserve. A Hawaii County Civil Defense overflight Thursday found the tip of the flow to be about 3.1 km (1.9 mi) upslope from the intersection of Highway 130 and Pahoa Village Road near the Pahoa Marketplace. There was no significant change in activity at Pu‘u ‘O‘o.
The level of the summit lava lake within Halema‘uma‘u Crater rose through the first part of the week, matching a general trend of summit inflation, and was about 43 m (140 ft) below the rim of the Overlook Crater on Thursday.
There was one earthquake reported felt in the past week on the Big Island. At 9:12 p.m. Dec. 4, a magnitude 2.2 earthquake occurred 6.4 km (4.0 mi) west of ‘Opihikao at a depth of 3.4 km (2.1 mi).
Visit the HVO website (http://hvo.wr.usgs.gov) for past Volcano Awareness Month articles and current Kilauea, Mauna Loa and Hualalai activity updates and more; call (808) 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov. Volcano Watch is a weekly article and activity update written by scientists at the USGS`s Hawaiian Volcano Observatory.