To the casual observer, lava that recently flowed into the outskirts of Pahoa might look a lot like the lava that grazed the village of Kalapana in November 1986 and completely overran it in 1990. In fact, these Kilauea flows were significantly different in most aspects that affect how far and how fast lava moves downslope.
To the casual observer, lava that recently flowed into the outskirts of Pahoa might look a lot like the lava that grazed the village of Kalapana in November 1986 and completely overran it in 1990. In fact, these Kilauea flows were significantly different in most aspects that affect how far and how fast lava moves downslope.
Theoretically speaking, the surface extent (how far) and advance rate (how fast) of lava is regulated primarily by three factors: eruption rate; lava temperature and, therefore, “crystallinity” at the time of eruption; and topography (slope of the land). Crystallinity refers to the abundance and types of phenocrysts (crystals that grow in magma before it erupts to the surface) and micro-phenocrysts (minute crystals that grow in a lava flow as it advances and cools) in lava.
Olivine, the first mineral to grow in magma as it rises into Kilauea’s summit reservoir system, crystallizes at a temperature below 1,215 degrees Celsius (2,219 degrees Fahrenheit). At lower temperatures, below 1,150 degrees Celsius (2,102 degrees Fahrenheit), the minerals pyroxene and plagioclase also crystallize along with olivine.
When lava is erupted, micro-phenocrysts of plagioclase and pyroxene form within the molten rock as it flows over the ground and cools. As crystallinity increases, the flow becomes more viscous (pasty) and eventually stalls and solidifies.
From 1986-92, lava flows were erupted from Kupaianaha, an active vent less than 12 km (7 miles) from Kalapana. During that time, eruption temperatures ranged from 1,155 to 1,170 degrees Celsius (2,111– 2,138 degrees Fahrenheit) and the lava contained few olivine crystals, about 1 mm (0.04 inches) in size.
Lava tubes from Kupaianaha carried lava down the steep southern flank of Kilauea. These tubes enabled efficient delivery of 300,000 to 400,000 cubic meters (390,000 to 520,000 cubic yds) of lava per day to the coastal plain at temperatures of 1,145 to 1,160 degrees Celsius (2,093 to 2,120 degrees Fahrenheit).
At those temperatures, the tube-fed flows that reached Kalapana still were relatively fluid and crystal-poor. This resulted in the fast-moving pahoehoe sheet-flows that quickly spread through Kalapana and covered the black sand beach at Kaimu Bay in 1990.
In contrast, the June 27 lava flows erupted from the northeast flank of Pu‘u ‘O‘o are moving down the crest of Kilauea’s East Rift Zone toward Pahoa, more than 20 km (12 mi) away. Since 2011, eruption rates have been estimated at about 175,000 cubic meters (230,000 cu yds) per day, the lowest sustained rate in more than 30 years of eruption, and the eruption temperatures have been 1,140 to 1,145 degrees Celsius (2,085 to 2,095 degrees Fahrenheit).
The June 27 lava flows contain a mix of olivine, plagioclase and pyroxene phenocrysts, often as crystal clusters 1 to 5 mm (0.04 to 0.2 in) in size. In contrast, the higher temperature Kalapana flows contained only olivine phenocrysts.
Despite its cooler temperatures and lower eruption rates, the June 27 lava flow traveled nearly twice the distance of the 1986 and 1990 Kalapana flows. But the Kalapana flows were cut short when they flowed into the ocean, so how much farther they could have traveled is not known.
As with the abrupt termination of the 1986 Kalapana-bound flows, the leading edge of the June 27 flow stagnated when lava was tapped to supply pahoehoe breakouts at higher elevations near Pu‘u ‘O‘o. The relative contribution of lava temperature, crystallinity, eruption rate and topography to this stagnation is now the subject of ongoing research. Whether additional lava will advance farther than the distance the June 27 flow already reached remains to be seen.
Based on our recent analyses of the June 27 lava flow, current eruption conditions do not favor a Kalapana-like scenario in which broad sheet-flows inundate large swaths of land. However, we must keep in mind that eruption conditions — for instance, eruption rate, lava temperature and vent location — can change unexpectedly. Because of this, the USGS Hawaiian Volcano Observatory continues to closely monitor Kilauea and will notify the public of any significant changes in the eruption.
Kilauea activity update
Kilauea’s East Rift Zone lava flow continues to feed three areas of breakouts near Pu‘u ‘O‘o. The breakout farthest downslope had reached to about 7 km (just more than 4 mi) northeast of Pu‘u ‘O‘o by Wednesday based on satellite imagery.
There have been no major changes at Kilauea’s summit vent, which continues to host an active lava lake. The lava lake level continues to fluctuate and was 42 m (140 ft) below the rim of the Overlook crater Thursday. One earthquake was reported felt on the Big Island this past week. At 5:08 p.m. Sunday, March 29, a magnitude 2.5 earthquake occurred 12 km (7.5 miles) north of Kailua-Kona at a depth of 13.6 km (8.5 miles).
Visit the HVO website (http://hvo.wr.usgs.gov) for past Volcano Watch articles, Kilauea daily eruption updates and other volcano status reports, current volcano photos, recent earthquakes and more; call (808) 967-8862 for a Kilauea summary update; email questions to askHVO@usgs.gov.
Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by scientists at the U.S. Geological Survey`s Hawaiian Volcano Observatory.