Weekly Volcano Watch: A laser's look into the lua reveals how pit craters grow

Reprinted from here.

Light detection and ranging (LiDAR) image of the southeast wall and currently active pit crater of Halema`uma`u. Image courtesy of Todd Erickson, Pacific GPS Facility SOEST University of Hawaii, Manoa.

This month, researchers from the University of Hawai`i teamed up with the Hawaiian Volcano Observatory staff to use laser-based technology to peer into the depths of a new pit in Halema`uma`u. What they saw was startling. The look revealed that the vent has a cavernous interior that dwarfs the size of the opening that we see at the surface. The cavern is approximately 200 m (650 ft) below the floor of Halema`uma`u, making it a dizzying 285 m (935 ft) below the now-closed Halema`uma`u overlook area.

To obtain the image, the UH researchers were using a technology called Light Detection and Ranging, or LiDAR, for short. By bouncing pulses of lasers off objects, LiDAR can determine the distance to out-of-reach objects. Readers may be familiar with similar technology used in the laser range finders employed by golfers, hunters, and builders. Simple laser range finders measure a single distance to an object. In contrast, scientist using LiDAR data can produce entire images, or models, of distant surfaces based on thousands of individual laser bounces.

The remarkable part of the image is that it reveals a very deep pit crater with dramatic overhanging walls near the surface. This is different from the steep and vertical walls of the larger Halema`uma`u and Kilauea caldera.

What the image actually reveals is a snapshot in the evolution of a Hawaiian pit crater. "Pit crater" is a general term used to describe the steep-sided, semi-circular, and flat-bottomed craters that are characteristic of the summit and rift zone areas of Kilauea and Mauna Loa volcanoes. Interchangeable terms for these features include, "collapse crater", and of course the eloquent Hawaiian name for a pit, "lua". But how are these craters created?

Looking into this deep hole created by a volcano may lead one to think that all the material was blasted out. But if this were the case, we would be able to see a vast amount of excavated material deposited around the rim of the pit. In fact, the amount of ejected material, or ejecta, surrounding Hawaiian pit craters is relatively small -- far less than the amount of material required to fill the hole back up. And, some Hawaiian pit craters do not have any ejecta surrounding them.

The answer to how pit craters form is being witnessed right now as the new vent evolves. Hawaiian pit craters form primarily through the evacuation, or loss, of magma somewhere beneath the vent. As magma evacuates from the plumbing system below, the conduits collapse and the vent floor sinks away. The walls may become overhung, since the interior of the pit expands as it drops. Eventually, the overhung portions of the rim collapse into the pit, and the characteristic near-vertical sides of the pit crater are formed.

Our observations of lava within the vent, data from instrumentation, and measurements of magma flux at the east rift zone near Kalapana, suggest that the amount of magma within the plumbing system of Kilauea has been reduced. This ebbing has caused the drop in the lava level and the growth of the cavern we now see. The recent pulses of ash-laden plumes issuing from Halema`uma`u have been caused by collapses of the pit's overhanging rim.

Of course, the drop in the vent floor, and ebb in the flow of magma within the system, does not necessarily mean the eruption is winding down. A characteristic behavior of Hawaiian pit craters is that the floor may refill with a lava lake, only to drain and collapse again and again. So the laser's look into the lua is certainly only a snapshot of the on-going evolution of Halema`uma`u.

Kīlauea Activity Update

Surface flows have been active on the pali within Royal Gardens subdivision throughout the past week, burning forest and one unoccupied structure. At the coast, the Waikupanaha and Kupapa`u ocean entries remain active and continue to produce steam plumes and small littoral explosions.

The vent at Kīlauea's summit was dark and quiet all week, producing only a very small quantity of rock dust from small collapses of the vent walls. The plume has been thin and wispy, and volcanic gas emissions have been relatively low. They are, however, still elevated above background levels, resulting in high concentrations of sulfur dioxide downwind.

One earthquake beneath Hawai`i Island was reported felt this past week. A magnitude-2.8 earthquake occurred at 10:38 p.m., H.s.t. on Thursday, July 9, 2009, and was located 3 km (2 miles) south of Holualoa at a depth of 36 km (22 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.

For more information on visiting Hawaii in general and touring Hawaii Volcanoes National Park in particular, please also visit www.lovingthebigisland.wordpress.com and www.tourguidehawaii.com.

The beginning of a new era—Kilauea's 1952 summit eruption

Reprinted from here.

Halema'uma'u 1952:

A single low lava fountain emitted a steady stream of gas when photographed by Fred Rackle on July 21, 1952, when Halema`uma`u Crater was more than twice as deep as it is at present. View is to the southwest.

The HVO Web site was recently revamped to make access to our increasing number of Webcams easier for About 20 minutes before midnight on June 27, 1952, almost exactly 57 years ago, Mrs. John Fox walked from the living room of her home on the east rim of Kilauea caldera into an adjoining room. She was instantly startled by a loud, whistling roar coming through an open window. Running back into her living room, she saw a bright orange glow lighting the night sky.

At about the same time, just down the road at Kilauea Military Camp (KMC), Colonel B.W. Rushton pointed out the bright glow to Hawaiian Volcano Observatory (HVO) staff member John Forbes, who quickly called Gordon Macdonald, then Scientist-in-Charge of HVO.

When John Forbes arrived minutes later at HVO, on the edge of Kilauea caldera, he was greeted by the top of a huge lava fountain rising above the rim of Halema`uma`u. The crater was then nearly 245 m (800 ft) deep—more than twice its current depth from the rim to the crater's floor. By the time Gordon Macdonald arrived at HVO some 10 minutes later, the fountain was no longer visible, but incandescent fragments could still be seen arcing out of the crater.

Quickly grabbing the necessary equipment, Macdonald and Forbes set out by car for Halema`uma`u Crater to make detailed observations. As they followed Crater Rim Drive down onto the western floor of Kilauea caldera—the section of road that is closed today due to ongoing summit activity—they encountered a choking, sulfurous fume cloud so thick that they could barely see the road.

The fall of tephra onto the road was so heavy that they were hard-pressed to keep the car moving forward as it plowed through the drifts of pumice. The hail of tephra onto the car, with pieces reaching up to 10 cm (4 inches) across, sand-blasted the car's exterior to the point that it later had to be repainted and have its windshield replaced.

Pressing onward, Macdonald and Forbes passed through the tephra fall and quickly walked to the southeast rim of Halema`uma`u, reaching it about 10 minutes past midnight. When they peered into the crater, they saw a continuous line of lava fountains, 790 m (2,600 ft) in length, crossing the entire crater floor from southwest to northeast and extending part-way up the northeastern crater wall.

For the most part, the individual fountains were 15 to 30 m (50 to 100 ft) in height, but a fountain 120 m (400 ft) high jetted up near the bottom of the southwestern wall of the crater—probably a diminished version of the same fountain, at more than 245 m (800 ft) in height, seen minutes earlier from HVO.

Though views were poor due to the heavy fume, brief glimpses of the crater floor showed that older spatter cones on the floor of Halema`uma`u had already been buried beneath a rising lava lake. This suggested that more than 3 million cubic meters (4 million cubic yards) of lava were erupted in the first half-hour of the eruption. It would take about six days for Kilauea's current east rift zone eruption to pump out that much lava today.

The eruption rate quickly declined after the initial outbreak, but lava fountains continued to play on the surface of the lava lake over the following weeks. By late summer 1952, activity had begun to decline, but the eruption persisted until November 10, when the last fountaining activity was observed.

Having erupted for 136 days, the 1952 summit eruption brought to an end, in grand fashion, any doubts as to whether or not Kilauea was still alive. Prior to 1952, Kilauea had been quiescent since October 1934, when the previous summit eruption had ended, and some had begun to think that Kilauea was dead. But frequent earthquakes and the occasional swelling and shrinking of the volcano over the intervening years told volcanologists otherwise. It was no great surprise, then, when the eruption finally occurred.

Followed by dozens of eruptions in the years since, the 1952 eruption undoubtedly ushered in the current era of volcanic activity at Kilauea. Today's ongoing summit and east rift zone eruptions are just the most recent in the string of eruptions that have followed since Mrs. Fox was surprised by the glow outside her living room window.

Kīlauea Activity Update

Surface flows in the Royal Gardens subdivision may have stagnated early this past week in response to a deflation-inflation (DI) event at Kīlauea's summit. Smoke continues to rise, however, from forested kipuka in the subdivision, indicating that at least some burning continues. At the coast, the Waikupanaha and Kupapa`u ocean entries remain active and continue to produce prominent plumes, accompanied by small littoral explosions, as lava spills into the ocean.

At Kīlauea's summit, the vent within Halema`uma`u Crater is still emitting elevated amounts of volcanic gas, resulting in high concentrations of sulfur dioxide downwind. Glow from the vent was visible at night through the past week, and rare views into the vent by HVO scientists found that the lava surface is still present about 205 m (675 feet) below the floor of Halema`uma`u Crater.

No earthquakes beneath Hawai`i Island were reported felt this past week.

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov. Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory.

For more information on traveling to Hawaii in general and exploring the Big Island's volcanoes in particular, please also visit www.tourguidehawaii.com and www.lovingthebigisland.wordpress.com.

Volcano Update: Quiescence in 1913 is similar to 2008 events

Reprinted from here.

The Eruption of Halema'uma'u as seen from Steaming Bluff, HVNP, August, 2008: Photo by Donald MacGowan

Quiescence in 1913 is similar to 2008 events

In most sciences, processes are investigated by identifying the factors that affect them and varying each factor, in turn, to determine its contribution. In field geology, this is difficult; instead, we compare and contrast events or locations to learn more about the processes. At Kīlauea, there is a long, well-documented history with which to compare and contrast current activities. Summit events at Kīlauea over the last year have been unique since 1924, but bear interesting similarities to lulls in lava lake activity prior to 1924.

It is well known that, until 1924, there was a nearly continuous lake of lava in Halema`uma`u Crater, which was less than half the diameter it is today. But "nearly continuous" means there were periods when the lava lake disappeared. Mid-1913 to late 1914 was one of those periods when the crater was filled with fume, but not lava. Fortunately, regular Hawaiian Volcano Observatory (HVO) reports described this lull.

In 1913, HVO was located where the Volcano House hotel is today. Lacking direct views into Halema`uma`u Crater, observers noted sounds and characteristics of the fume coming from the pit to describe its behavior.

Reports of glow were infrequent, but descriptions of noises from the crate-blowing, coughing, booming, hissing, rumbling, grumbling, puffing, and breathing-were common. Rock slides, which were frequent and audible, sometimes produced dust clouds.

"During the last three months the only marks of activity which have fluctuated have been noises of blowing and rumbling, greater or less suffocating quality to the fumes when breathed, and very rare glimpses of flame seen two or three times at night." (HVO report, August 18, 1913).

Through September, the noises increased in intensity, and some glow was observed. Pele's hair was frequently found downwind of the crater and, when the fumes cleared, glimpses of a lava vent deep in Halema`uma`u Crater could be seen.

By October 20, 1913, Halema`uma`u Crater was considered to be in a minor eruptive phase. The crater was emitting much greater volumes of fume than in August. Sounds resembling "swashing liquid" suggest the continued existence of a lava lake, even when it was obscured by fume. A glow-lit fume cloud was a frequent sight over the crater at night.

Activity decreased through the end of 1913, and Halema`uma`u finished the year in a "semi-dormant" state, with a crater shaped like a huge funnel about 200 m (600 ft) deep and a thickly crusted lava pool in its bottom. Vigorous lava lake activity did not resume until late 1914.

Jump ahead to 2008. HVO reports have been describing many of the same characteristics. Few views of a lava pond have been recorded, but blowing and booming sounds, rock falls, and dust plumes have been common. Explosions were common in much of 2008, and some were energetic enough to erupt material to the crater rim.

The 1913-14 lull in activity and the currently elevated summit activity both result from lava being at similar shallow depths below Halema`uma`u Crater. In the early part of 1913, lava dropped to that level. In early 2008, magma rose to a similar depth.

The 2008 activity produced small amounts of tephra, often including Pele's hair. The 1913-14 lull also produced notable amounts of Pele's hair, but production of other tephra was not recorded.

Throughout both events, progress is highly variable. The overall rise of lava in the crater during 1913 and 1914 was halting, with episodes of rise repeatedly cut short with episodes of subsidence. Similarly, the 2008 activity changes several times a week, with lava interpreted to be rising and falling within the conduit below the vent.

In both cases, shallow magma produced elevated SO2 emissions and glow from the vent. "Fumes continue to pour out without abatement" (HVO report, February 4, 1914). Observers commonly described the fume as being difficult to breathe in 1913. Respiratory protection is required to work in the fume emitted today but probably wasn't necessary in earlier years.

HVO continues to monitor Kīlauea's activities and we hope to learn more by comparing recent events with past volcanic activity.

Activity update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is emitting elevated amounts of sulfur dioxide gas and producing small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. A collapse deep within the vent on Wednesday, February 4 produced a robust brown plume and appeared to reopen the conduit, filled with rubble since early December. Views inside the vent the next day with a thermal camera showed a small, crusted lava pond more than 100 yards below the vent rim.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava erupting from the Thanksgiving Eve Breakout (TEB) vent at the eastern base of Pu`u `Ō`ō continues to flow to the ocean at Waikupanaha through a well-established lava tube. Breakouts from a western branch of the lava tube were active on the coastal plain near the National Park boundary early in the week and also continued to feed the small ocean entry near Waha`ula. A deflation-inflation cycle beginning February 3 led to a short-term reduction in lava supply to the flow field. Surface flows and ocean entries were inactive on Thursday, February 5, and will probably resume shortly.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. The Waikupanaha delta has collapsed many times over the last several months, with three of the collapses resulting in rock blasts that tossed television-sized rocks up onto the sea-cliff and threw fist-sized rocks more than 200 yards inland.

Do not approach the ocean entry or venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Call Hawai`i County Civil Defense at 961-8093 for viewing hours.

Mauna Loa is not erupting. No earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano, combined with slow eastward slippage of its east flank.

Three earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-3.2 earthquake occurred at 3:37 p.m., H.s.t., on Friday, January 30, 2009, and was located 2 km (1 mile) east of Pahala at a depth of 10 km (6 miles). A magnitude-3.4 and a magnitude-3.5 earthquake occurred at 7:12 and 7:17 p.m., respectively, on the same Friday and were located 7 km (4 miles) west of Kalapana at a depth of 9 km (6 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.

For more information on traveling to Hawaii in general and seeing the volcanoes of the Big Island in particular, please visit www.tourguidehawaii.com and www.tourguidehawaii.blogspot.com.

New Video of Kilauea Eruptions on the Big Island of Hawaii

A montage of some of my favorite footage that Frank and I have shot of the Kilauea eruption, from the active vents at Pu'u O'o and Kupaianaha to the ocean entry at Waikupanaha, as well as day and night time footage of the summit eruption at Halema'uma'u. Sit back, turn up the speakers and enjoy--I've even recorded a new piece of music to go with it.

Produced by Donald B. MacGowan; videography by Frank Burgess and Donald MacGowan; Original music written and performed by Donnie MacGowan. For more information about traveling the Big Island in general and exploring Hawaii Volcanoes National Park in particular, visit www.tourguidehawaii.com and www.lovingthebigisland.wordpress.com.

More information about the producer can be found here and here.

Volcano Watch: Where did the rest of the rocks go? More went down than up ...

Reprinted from here.

Now that the 2008 Halema`uma`u eruption has ended (or is in repose), the total volume of solid material (tephra) thrown out from the new vent can be estimated. This volume, though tiny, is interesting, for it bears on the origin of the vent itself.

Calculation of the volume is complicated, however. We did it in two parts, one for the 8 explosive eruptions (March 19, April 9 and 16, August 1 and 27, September 2, and October 12 and 14) and the other for the nearly continuous ejection of tephra between those events. Each approach first calculates the mass (weight) of the ejecta, from which the volume can be determined.

We used a mathematical model, developed 20 years ago for eruptions hundreds of times larger than ours, to estimate the weight of tephra ejected during the 8 explosive eruptions. For each one, we weighed all the tephra that landed in 10 or more small areas, each generally 1 square meter (10.8 square feet) or less. Weights from these areas were then fed into the model to calculate the total weight of all the tephra erupted. The volume can be calculated by knowing the density of the tephra. A weight of 1,000 kg (2,200 pounds) is approximately equivalent to a volume of 1 cubic meter (1.3 cubic yards).

The largest explosive eruption, on September 2, produced 800 cubic meters (1,050 cubic yards), about the volume of the display section of the Jaggar Museum. The smallest, on October 14, ejected about 7 cubic meters (9 cubic yards), about half of a modest bathroom with shower. The total volume ejected by all 8 explosive eruptions is about 1,640 cubic meters (2,150 cubic yards).

These were tiny events! For comparison, the volume of ejecta in the largest lava fountain of the 1959 Kīlauea Iki eruption was about 400 times the volume of the September 2 eruption. The two largest known explosive eruptions from Kīlauea, about 1200 and 400 years ago, each had a volume more than 25,000 times that of the September 2 event.

The volume of the nearly continuous tephra fall between the 8 main events was calculated from the weights that fell into 10 plastic buckets on the ground between the vent and the parking lot. Each morning, the contents of the buckets were weighed. For several days, we calculated an average ratio between the weight in the buckets and the total weight of the deposit by using the tedious mathematical model. Using this ratio, we could calculate the deposit weight from the daily collections. A volume was estimated from that weight. The volume ejected between the explosive eruptions is only about 300 cubic meters (390 cubic yards), 18 percent of the volume erupted by those much larger events.

The total volume of ejecta from the 2008 eruption is about 1,940 cubic meters (2,540 cubic yards), about three times the volume of the Jaggar Museum display area.

The tephra consists of two different materials. One, derived from the lava itself, is called juvenile; Pele's tears and spatter are examples. The other, broken from older rocks exposed in the walls of the vent, is called lithic. Ongoing studies show about equal amounts of juvenile and lithic tephra in the deposits, about 970 cubic meters (1,270 cubic yards) each.

Now the fun begins. The volume of the crater created at the vent is 200,000-300,000 cubic meters (260,000-390,000 cubic yards), but the volume of the lithic ejecta is only 970 cubic meters (1,270 cubic yards), a discrepancy of 200-300 times! Clearly, most of the rocks removed to form the vent crater must have collapsed into the underground rather than being tossed onto the ground surface.

What did the rocks collapse into? Was it a cavity, did they fall onto a "conveyor belt" that carried them away, or what?

Underground voids are anathema to many geologists. But, limestone caves exist to depths of 2.2 km (7,200 ft), and deep mines go down to nearly 3.5 km (11,500 ft). Why couldn't temporary cavities a few hundred meters deep exist in Kīlauea? The deep mines are engineered, but Nature is a better engineer than Homo sapiens.

Pit craters, as along the Chain of Craters, are thought to form by collapse into a void. Perhaps we have witnessed the formation of a small pit crater, twice the diameter of Devil's Throat, without realizing it.

For more information on traveling to Hawaii in general and touring the Big Island in particular, please visit www.tourguidehawaii.com and here.

Activity update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is emitting elevated amounts of sulfur dioxide gas but producing no ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava erupting from the Thanksgiving Eve Breakout (TEB) vent at the eastern base of Pu'u 'O'o continues to flow to the ocean at Waikupanaha through a well-established lava tube. Beakouts from the lava tube were active in the Royal Gardens subdivision and on the coastal plain in the past week. Ocean entry activity has continued throughout the past week, with a minor short-term reduction in activity following a deflation-inflation cycle on December 31-January 1.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. The Waikupanaha delta has collapsed many times over the last several months, with three of the collapses resulting in rock blasts that tossed television-sized rocks up onto the sea-cliff and threw fist-sized rocks more than 200 yards inland.

Do not approach the ocean entry or venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Call Hawai`i County Civil Defense at 961-8093 for viewing hours.

Mauna Loa is not erupting. Six earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano, combined with slow eastward slippage of its east flank.

Two earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.8 earthquake occurred at 5:53 a.m., H.s.t., on Monday, January 5, 2009, and was located 5 km (3 miles) northeast of Na`alehu at a depth of 12 km (8 miles). A magnitude-2.1 earthquake occurred at 1:17 p.m. on Wednesday, January 7, and was located 8 km (5 miles) northeast of Waiki`i at a depth of 14 km (9 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.

Weekly Volcano Watch!

Reprinted form here.

Halema`uma`u engine shifts gears, but keeps on chugging

Photos, taken by HVO's webcam on November 17th illustrate the new behavior of the summit eruption plume, which this week began oscillating between strong and robust (left), and weak and wispy (right).

For the past month, Kīlauea's summit eruption has been steadily chugging along. Clattering sounds issue from the Halema`uma`u vent as gas pulses forth, forming a thick plume that rolls into white billows high above the caldera. On most days, the plume rises and turns above the summit, gently drifting southward and darkening the Ka`u landscape. In the distance, an endless train of fume wraps around the flanks of Mauna Loa, destined for Kona and other points on the island chain.

Since mid-October, this scene has been relatively steady. But on Monday, November 17th, something changed. The thick white plume that we have become accustomed to seeing suddenly vanished, leaving only transparent trails of fume issuing from the vent. It appeared as though the summit activity had stopped—the chugging engine had seized. But, just as suddenly as it paused, it resumed a few minutes later, and the thick plume returned, puffing high above the caldera. This cycle of robust and wispy plumes occurred several more times on Monday and into the next day.

On Tuesday morning, HVO geologists made their way to the crater's edge and were standing above the vent through four of these plume transitions. Instead of a continuous flow of fume and occasional clatter, they witnessed something far more curious. When the plume became weak and wispy, the faint roar of surf, usually a common sound, was barely audible. Then, suddenly, they heard the loud and intimidating sound of breaking glass, followed by the rushing return of a thick white plume.

During these changes, cameras captured images and instruments recorded temperatures as glow returned to the vent. The glow intensity and associated temperatures were the highest observed since mid-October.

The amount of material ejected onto the crater rim also increased to its highest level since mid-October. This material largely consists of Pele's hair and other glassy fragments suggestive of fresh lava.

So, what is happening at the vent and why has it changed? Our explanations of natural phenomena are always working hypotheses that are refined as more data become available. At this stage, our data suggest that lava may be pistoning (rising and falling) within the vent.

When pistoning occurs, lava rises within the conduit to a level perhaps within 100 meters (300 feet) of the vent rim. As the lava cools, a crust forms on its surface. This crust can impede the flow of gas, causing pressure to build within the lava. When enough pressure is built to break the crust, gas can rush forward. The reduction in gas pressure causes the lava piston to drop down within the vent, and the cycle starts again.

Scientists at HVO have witnessed lava pistoning within vents during other eruptions on Kīlauea. For example, seismic tremor recorded at the summit in recent days is reminiscent of tremor produced at Pu`u O`o several years ago, when lava filled and drained from vents within its crater.

The sound of breaking glass heard within the vent may be caused by shattering of the glassy crust on the lava-piston's surface. The increase in glassy lava fragments deposited on the rim of Halema`uma`u is probably the result of this sequence.

Periods of intense glow observed at night could also be explained by the pistoning. When the crust breaks up and the lava level drops, red-hot molten lava and incandescent vent walls are exposed, increasing the intensity of the glow.

An explanation for changes deep within the volcano causing this pistoning behavior is more ambiguous. Whatever the reasons are for the shift in summit activity, we are sure that the engine is still chugging.

Activity update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. The have been several small ash-emission events from the vent, lasting only minutes, in the last week. For a few days mid-week, there were several brief periods of decreased plume vigor lasting minutes to hours. During these periods, the plume was the weakest it has been since the vent opened last March.

Pu`u `Ō`ō continues to produce sulfur dioxide at rates higher than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava continues to erupt from the Thanksgiving Eve Breakout (TEB) vent and flows toward the ocean through a well-established lava tube. Activity at the Waikupanaha ocean entry has fluctuated over the past week, with periods of small littoral explosions and a voluminous plume, followed by periods of no explosions and a wispy plume. Part of these fluctuations may have occurred in response to a deflation-inflation (DI) event at Kilauea's summit on November 16-17. A western branch of the tube, which diverges from the main TEB tube at the top of the pali, continues to supply lava to breakouts on the coastal plain. These breakouts are scattered along the western margin of the TEB flow field and are slowly marching southward toward the National Park boundary.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check the Civil Defense Web site (http://www.lavainfo.us) or call 961-8093 for viewing hours.

Mauna Loa is not erupting. Two earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

There were no felt earthquakes reported on Hawai`i Island for the past week.

Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. 

For more information on visiting Hawaii in general and touring the Big ISland in particular, go to www.tourguidehawaii.com and www.lovingthebigisland.wordpress.com.

Sloshing lava lake viewed within Halema'uma'u vent

Reprinted from here.

This near-vertical view reveals a vigorously bubbling lava surface below the rim of the vent within Halema`uma`u crater. Continuous spattering was casting globs of lava across the lake surface and onto the conduit walls.

For the first time since the new vent opened in Halema'uma'u Crater on March 19, HVO scientists in a helicopter hovering over the crater were able to see the surface of a sloshing 50 m (160 ft) diameter lava lake about 100 m (330 ft) below the vent rim. HVO scientists have speculated that a lava pond existed a few hundred meters below the vent, but have not been able to get visual confirmation until this morning.

A second viewing early this afternoon revealed a roiling pond with multiple bursting bubbles changing into a central upwelling circulation pattern. The lake level dropped slightly before the cycle restarted. This behavior has been witnessed before, most recently in Pu'u 'O'o vents and the July 21 lava ponds on Kilauea's east rift zone, and is known as "gas pistoning." One model explains pistoning as small gas bubbles coalescing into larger bubbles beneath a crust on a lava pond, rising to the surface, and then bursting. The released pulse of hot gas carries rock dust from the collapsing vent walls, bits of the lava lake crust, and small amounts of spatter.

The Halema'uma'u vent has produced six significant explosive eruptions in the past 5.5 months, most recently on September 2, 2008 at 8:13 p.m. H.s.t., during which noteworthy amounts of fresh lava spatter and lithic material (rock fragments and dust) were ejected on to the crater rim. Just prior to this event, incandescence from the vent was almost nonexistent except for brief pulses of glow.

Nearly eight hours later, Kilauea's summit abruptly inflated, signaling the end of 39 hours of deflation. Summit deflation-inflation (DI) events have been observed at least 20 times since the Halema'uma'u vent opened. Each DI event has been interpreted as the fall and subsequent rise in magma levels beneath the summit.

Less than 8 hours after inflation started, episodic tremor bursts began which are visible at night as pulses of bright incandescence every 5-6 minutes. Episodic tremor bursts have been a nearly constant feature of the Halema'uma'u vent over the past few months and were one of the early pieces of evidence pointing toward a gas pistoning source.

This unusually bright incandescence over the past two nights and the volume of material erupted on September 2 are consistent with a lava surface at relatively shallow depths beneath the vent. Molten lava is not directly visible from the Jaggar Museum overlook, but that vantage point provides excellent views of the glowing vent at night.

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