Quickening eruptive ‘pulse’ spawns Kahauale‘a flow
Over the past six months, the pace of Kilauea’s 30-year-long ongoing eruption has quickened. This follows the quietest period — spanning most of 2012 — of the eruption yet recorded. In the east rift zone, this quiet period was characterized by persistent Peace Day flow breakouts scattered on the coastal plain that failed to reach the ocean all summer.
Along with other lines of evidence, this stall of the flow advance suggested that the eruption rate was well below the long-term average. Then, in late November, the flow became more cohesive, advanced to the coast, and entered the ocean. The entry plumes, while very weak at first, became stronger and new entry points developed, indicating that the eruption rate was increasing.
At the same time, lava began to erupt from spatter cones at Pu‘u ‘O‘o. The crater filled slowly and, in January 2013, began to overflow its eastern rim. One spatter cone, on the northeast edge of the crater floor, developed into a low shield that stood above and eventually buried the adjacent crater rim. On Jan. 19, lava from that shield began to spill down the northeast flank of Pu‘u ‘O‘o cone, starting a new lava flow informally named the Kahauale‘a flow.
Flowing continuously since, the front of the Kahauale‘a flow has traveled about 2.8 miles to the northeast over ‘a‘a flows erupted from Pu‘u ‘O‘o in the early 1980s and pahoehoe and ‘a‘a flows erupted in 2007. The flow has slowed but widened over the past week. It traverses the Kahauale‘a Natural Area Reserve and extends a short distance into the Wao Kele o Puna Forest Reserve.
What does all of this mean?
Over the 30-year duration of the current east rift zone eruption, most lava flows have gone south toward the coast; flows north of the rift zone have been infrequent. During 1983 to 1986, there were several short-lived flows associated with fountaining phases of Pu‘u ‘O‘o that advanced parallel to, and north of, the rift zone; but they stopped when the fountaining ceased at the end of each episode. Flows from Kupaianaha in the late 1980s were prevented from going north by these older Pu‘u ‘O‘o flows.
In the summer of 2007, a new fissure that opened on the east flank of Pu‘u ‘o‘o sent lava flows initially toward the northeast. A few months later, a vent wall near the source ruptured and diverted lava to the south again. While these flows were advancing north of the rift zone, Puna residents became worried by the bright glow in the sky and the smell of wood smoke. HVO published a lava flow hazard assessment specifically addressing possible future lava flow directions and speeds (http://pubs.usgs.gov/of/2007/1264/of2007-1264.pdf).
Like these other flows, the Kahauale‘a flow is advancing north of the rift zone but is blocked to the south by the 2007 lava. The main difference between the 2007 flows and the Kahauale‘a flow, however, is in supply rate of lava that fueled each flow. In 2007, these were the only active flows and they were fed at a supply rate slightly higher than the long-term average for this eruption. On the other hand, the Kahauale‘a flow is fed by less than half of the long-term average supply rate while the Peace Day flow is fueled by the rest.
As it was during the 2007 eruption, there is a distant possibility that the Kahauale‘a lava flows will continue to advance to the northeast. Over the past two months, the flow has advanced irregularly but at an average rate of 230 feet per day. Depending on exactly where the flows enter the forest, they could advance toward populated areas. The flows, however, would take months to reach these populated areas if — and this is a big “if”— they continue to advance at the current average rate. A lot could happen to slow or stop the flow between now and then.
Island residents can take comfort in knowing that, during the past 30 years, no other lava flows on the north side of Kīlauea’s East Rift Zone have ventured very far to the north — and that Hawaiian Volcano Observatory scientists are keeping close watch on the Kahauale‘a flow and will continue to update emergency managers and the public with the latest information.
Kilauea activity update
A lava lake within the Halema‘uma‘u Overlook vent produced nighttime glow that was visible from the Jaggar Museum overlook and via HVO’s webcam during the past week. The lake level fluctuated in response to summit deflation-inflation cycles, ranging between about 80 to 200 feet below the floor of Halema‘uma‘u.
On Kilauea’s east rift zone, breakouts from the Peace Day tube remain active above and at the base of the pali and on the coastal plain. Small ocean entries are active on both sides of the Hawaii Volcanoes National Park boundary. In addition, the Kahauale‘a flow, fed directly from a spatter cone on the northeastern edge of Pu‘u ‘O‘o’s crater floor, continues to advance slowly toward the northeast across a plain of 1980s-era ‘a‘a flows. The flow had traveled about 2.8 miles when last measured on March 22.
There were no felt earthquakes in the past week on the Island of Hawaii.
Visit the HVO website (http://hvo.wr.usgs.gov) for Volcano Awareness Month details and Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes, and more; call 967-8862 for a Kilauea summary; 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.
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