Kilauea volcano update: Summit lava lake continues to drop, risk of explosions increases
Thu, 10 May 2018, 05:4805:48 AM | BY: T
Ash column rises from the Overlook crater at the summit of Kīlauea Volcano. HVO's interpretation is that the explosion was triggered by a rockfall from the steep walls of Overlook crater. The photograph was taken at 8:29 a.m. HST from the Jaggar Museum overlook. The explosion was short-lived. Geologists examining the ash deposits on the rim of Halema‘uma‘u crater found fresh lava fragments hurled from the lava lake. This explosion was not caused by the interaction of the lava lake with the water table. When the ash cleared from the crater about an hour after the explosion, geologists were able to observe the lava lake surface, which is still above the water table. (image: HVO / USGS)
The summit lava lake inside Halema'uma'u crater continues to drop and the summit continues to deflate. As of yesterday evening, the lava lake's surface was 295 m (970 ft) below the floor of the crater, leaving a deep funnel. Lava is no longer visible on the webcam images.
Thermal view of the pit crater where the lava lake used to be, no longer visible as of 10 May morning (image: HVO / USGS)
At about 8:32 local time yesterday morning, a large rockfall from the steep crater walls into the retreating lake triggered an explosion that generated an ash column above the crater (image); the ash was blown toward the south-southwest. Rockfalls and explosions that produce ash columns are expected to continue.
Warning of phreatic explosions
However, the volcano observatory now warns that as the magma column in the summit reservoir connecting to the lava lake continues to drain and drop, the risk of potentially large explosions increases. This will be especially true if the surface of the magma column drops beneath the ground water table under the caldera floor, which would allow water to seep into the hot conduit, and likely trigger violent steam-driven (phreatic) explosions, perhaps similar to those observed in 1924, when violent phreatic activity destroyed the pre-1924 lava lake and excavated the Halema'uma'u crater as it was known after 1924.
from the Kilauea Volcano Activity Notice 20180509_0802:
"Debris expelled during such explosions could impact the area surrounding Halemaʻumaʻu and the Kīlauea summit. At this time, we cannot say with certainty that explosive activity will occur, how large the explosions could be, or how long such explosive activity could continue."
Ballistic projectiles hazard
"During steam-driven explosions, ballistic blocks up to 2 m (yards) across could be thrown in all directions to a distance of 1 km (0.6 miles) or more. These blocks could weigh a few kilograms (pounds) to several tons.
Smaller (pebble-size) rocks could be sent several kilometers (miles) from Halemaʻumaʻu, mostly in a downwind direction.
"Presently, during the drawdown of the lava column, rockfalls from the steep enclosing walls of the Overlook crater vent impact the lake and produce small ash clouds. These clouds are very dilute and result in dustings of ash (particles smaller than 2 mm) downwind.
"Should steam-driven explosions begin, ash clouds will rise to greater elevations above ground. Minor ashfall could occur over much wider areas, even up to several tens of miles from Halemaʻumaʻu. In 1924, ash may have reached as high as 20,000 feet above sea level. Small amounts of fine ash from these explosions fell over a wide area as far north as North Hilo (Hakalau), in lower Puna, and as far south as Waiohinu.
"Gas emitted during steam-drive explosions will be mainly steam, but will include some sulfur dioxide (SO2) as well. Currently, SO2 emissions remain elevated.
"Steam-driven explosions at volcanoes typically provide very little warning. Once the lava level reaches the groundwater elevation, onset of continuous ashy plumes or a sequence of violent steam-driven explosions may be the first sign that activity of concern has commenced.
"Kīlauea's lava lake began to drop on May 2, 2018. From its peak on May 2 to the most recent measurement at 9 pm on May 6, the lava lake surface dropped a total of more than 200 m (656 ft). The subsidence was at a relatively constant rate of about 2 meters (yards) per hour.
Measurements of subsidence have not been possible since May 6 because of thick fume and the increasing depth to the lava surface. However, thermal images indicate continued lowering of the lake surface since that time, consistent with deflationary tilt recorded at Kīlauea's summit. Therefore, we infer that the lake surface continues to drop at roughly the same rate. So, while HVO cannot report exact depths of the receding lava lake, we can monitor the overall trend.
Earthquake activity in the summit remains elevated. Many of these earthquakes are related to the ongoing subsidence of the summit area and earthquakes beneath the south flank of the volcano." (HVO / USGS)
Thu, 10 May 2018, 05:34
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Wed, 9 May 2018, 19:00