# Volcano Watch — How long will the current eruption last?

March 10, 2005

The current eruption at Kīlauea is 22 years old and counting. Residents in the down-wind direction have probably become tired of the vog and would like the eruption to end. How long can an eruption last?

The longest historical eruption of Kīlauea prior to the current eruption was of lava lake activity at the summit, which lasted for nearly 20 years in the early 1800s. In more recent times, the activity at Mauna Ulu, from 1969 to 1974, dominated Kīlauea's landscape until the current eruption at Puu Oo.

USGS colleagues have studied the prehistoric record of Kīlauea and found that a summit eruption near Nahuku (Thurston lava tube) may have lasted 50 to 60 years! The eruption originated just east of Kīlauea Iki and sent flows downslope until it reached the sea at Kaloli point in Hawaiʻian Paradise Park. An estimated volume of 5.2 cubic kilometers (1.25 cubic miles) of lava was erupted, and the area covered is roughly 430 square kilometers (166 square miles).

What can we learn from Kīlauea's older and larger sibling, Mauna Loa? According to historical record, Mauna Loa has had summit activity that lasted for 6 years and flank activity for over one year.

Our research into the prehistoric record reveals that eruptions at Mauna Loa could have lasted more than a century! Radiocarbon age-dating of lava flows from the summit of Mauna Loa suggests sustained activity from 1,000 to 1,500 years before the present, or calendar dates of A.D. 1100 to 650. This period coincides with the arrival of Hawaiʻians to the islands. Furthermore, our geologic mapping shows that both the summit and rift zones were simultaneously active.

The area impacted by the prehistoric summit activity includes the east and west flanks of Mauna Loa directly downslope of Mokuaweoweo, Mauna Loa's summit caldera. In addition, the flows inundated the northwest flank, Kapapala Ranch and Forest Reserve to the east, Pohakuloa Training Area to the northwest, and Devils Country, or Keauhou 2, to the west, otherwise known as the saddle between Mauna Loa and Hualālai.

Lava flows from the summit also reached the sea at Kamehame on Kīlauea's southeast coast, 47 kilometers (29 miles) away. Another summit flow, traveling in the direction of Puako (Mauna Lani), is 57 kilometers (35 miles), one of the longest flows on record. By comparison, Mauna Loa's 1880 flow, the source of Kaumana Cave (above Hilo), is 47 kilometers (29 miles) long.

The area covered during the prehistoric period is 640 square kilometers (247 square miles) and constitutes an estimated volume of between 5.6 to 7.7 cubic kilometers (1.3 to 1.8 cubic miles). For some residents of Hawaii, the eruption has become tiresome, and they wish the activity would stop. One has to be careful of what one wishes for, however. The current eruptive activity is in a rather benign place in Hawaii Volcanoes National Park; the lava flows are not threatening any developments. Based on long-term monitoring, we know that the magma supply to Kīlauea is fairly constant over the long term.

If the eruption were to shut off, the magma supply to the volcano would continue. Eventually the influx of magma into the volcano would create pressure and result in a new outbreak. This outbreak could be in a remote location or migrate to where it threatens communities on the flanks of the volcano. So how long will the current eruption last? Well, if we rely on the geologic record, it could last several more decades or even a century!

### Volcano Activity Update

Eruptive activity at Puu Oo continues. All vents inside Puu Oo crater were incandescent this past week, producing bright glow on clear nights.

The PKK flow continues to host substantial breakouts from atop Pulama pali to the coastal plain. A "gorgeous" open channel lava flow on the east branch of the PKK flow was widely visible between 1,400 and 800 feet elevation on March 8. Two ocean entries are currently active at East Laeapuki and Kailiili; the West Highcastle entry ceased activity earlier this week. East Laeapuki and Kailiili entries are about 3.5 km (2 miles) and 7 km (4.5 miles) respectively from the ranger shed. Expect a 2-to-3 hour walk each way and remember to bring lots of water. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.

During the week ending March 10, four earthquakes were felt on the island. The first was a magnitude-3.1 quake at 4:20 pm on March 5. It was located 4 km (3 miles) southeast of Puu Oo vent at a depth of 9 km (5.7 miles), and was felt in Hilo and Sea View Estates. Two earthquakes northwest of Loihi Seamount on March 8 were felt on the southern part of Hawaiʻi island. A magnitude-4.2 quake 16 km (10 miles) northwest of Lo`ihi at 7:26 am was followed by a magnitude-3.3 quake at 7:27 am. The events occurred at a depth between 17 and 19 km (11-12 miles). A magnitude-3 quake at 6:45 am on March 10 was located 8 km (5 miles) north of Kalapana at a depth of 2.4 km (1.5 miles). It was felt by residents at Black Sands, Leilani Estates, and Sea View Estates.

Mauna Loa is not erupting. The summit region abruptly stopped inflating at the end of January and then started inflating again in mid to late February. Since July 2004, the rate of inflation and number of deep earthquakes has increased. Weekly earthquake counts have varied from 5 to over 150 in the last half of 2004 but have been less than 10 since the beginning of 2005. During the week ending March 10, only five earthquakes were recorded beneath the volcano.