Volcano Watch — Lava meets the sea--again

Ka`ili`ili, just west of the site of Waha`ula, is a longer haul-7.5 km (4.7 mi) from the ranger shed.

Since November 1986, lava flows from the Pu`u `O`o-Kupaianaha eruption have entered the ocean almost 70 percent of the time, by far the longest such interval in Hawai`i in the past 500 years. The last few years, however, have seen a decline in ocean-entry viewing opportunities. This falling-off was due to prolonged periods when lava flows extended only a few kilometers from Pu`u `O`o.

In late 2003 and early 2004, new vents opened on the southwest flank of Pu`u `O`o, robbing supply from the existing Mother's Day tube. The new vents erupted sporadically, leaving the flows insufficient time to develop a stable lava tube to the coast. The Banana flow, an offshoot of the Mother's Day tube, finally regained the coast at the end of last May, but the entry survived only two months. By July, the Prince Kuhio Kalaniana`ole (PKK) tube, fed by one of the new vents, gained ascendancy and, in November, sent its first flow to the ocean.

The current ocean entries are fed by widely separated arms of the PKK flow, which splits into three main branches above the top of Pulama pali. As of last week, surface flows were breaking out of the PKK tube all the way from the 2,300-ft elevation down to the coast. The pali, streaked with incandescent flows, makes for spectacular nighttime viewing.

Unfortunately, all the surface activity does not bode well for the longevity of the ocean entries. An entry needs a stable supply line-a tube that isn't leaking lava flows in every direction-to survive.

After 18 years of ocean entries, 230 ha (570 acres) new land has formed. This is a net value that does not include new land claimed by collapse of active benches or by wave erosion of inactive ones. In some years we've recorded a net decrease in the total area of new land, even though flows entered the ocean the entire year.

Both the steep offshore slope and the exposure of the coastline to storm surf have contributed to the slow rate of building coastal real estate. The greatest area of new land was formed during 1990 and 1993, when lava filled the two largest embayments on the coastline, at Kaimu and Kamoamoa, respectively.

New land forms as lava deltas build seaward over steep slopes of unconsolidated lava fragments. These submarine slopes are prone to slumping, which removes support for the active, leading edge of the lava delta, or "bench." The catastrophic collapse of a bench can submerge several hectares of land in a matter of minutes or hours. Large collapses commonly trigger violent steam explosions when the severed lava tubes are exposed to the surf. Not all bench collapses are dramatic, however. Small, piecemeal collapse has been the dominant process at many benches. All are dangerous- heed the National Park warning signs.

Ocean entries can also create beaches. As lava enters the water, its surface quickly cools and fragments, creating the famous black sand of Hawai`i. The sand is carried to the southwest by longshore currents. Kīlauea's wave-battered coastline has few places sheltered enough to retain sand, so most of the black sand beaches that have formed during this eruption soon wash away. But if you walk out to the sea cliff where Chain of Craters Road follows the coast, you'll spot pockets of fresh black sand wherever there's a small bay.

The PKK flow has a history of rapid changes in vigor, so if you've been thinking about seeing an ocean entry up close and personal, now's the time!

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. At least four of the vents inside Pu`u `O`o crater have been spattering frequently since February 1, producing a bright glow from the crater on clear nights. Thus far, the crater vents have not produced any lava flows. The MLK vent area, at the southwest base of the cone, intermittently erupts small Pāhoehoe flows that stack up close to the vent.

The PKK flow continues to host substantial breakouts from the 2,300-ft elevaton to the coastal plain. Lava entered the ocean at West Highcastle on January 27, and at Ka`ili`ili on January 31. The closest activity to the end of Chain of Craters Road, in Hawai`i Volcanoes National Park, is at West Highcastle, 2.6 km (1.6 mi) from the ranger shed. Expect a 1-to-1.5-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.

Four earthquakes were felt during the week ending February 2 on Hawai`i Island. Two occurred within 5 km (3 miles) of Kīlauea summit at 4:44 p.m. and 8:27 p.m. on January 27. The magnitude 2.6-2.7 earthquakes were located shallower than 5 km (3 miles) and were felt in the Volcano Golf Course. A magnitude-2.5 earthquake occurred between Kawaihae and Waimea at a depth of 5 km (3 miles) at 7:37 a.m. on January 28. This quake was felt in Waimea. A magnitude-3.1 earthquake, 9 km (6 miles) deep, located near Pu`u `O`o, and occurring at 3:25 a.m. was felt in Volcano.

Over the last two weeks, the Kīlauea summit area has been unusually active. Nearly one hundred shallow earthquakes of magnitude 3 or less have occurred beneath a triangular area extending from Kīlauea summit south to Halape and Poliokeawe. As measured by GPS, extension across Kīlauea caldera has accelerated over the same period.

Mauna Loa is not erupting. The summit region continues to inflate. Since July 2004, the rate of inflation and number of deep earthquakes has increased. Weekly earthquake counts have varied from 5 to over 150, but have been low for the past four weeks. During the week ending January 27, six earthquakes were recorded beneath the summit area. Nearly all are 30 km (18 mi) or more deep, and most are the long-period type, with magnitudes less than 3.