Volcano Watch: Remembering The Thanksgiving Eve Breakout From 2007November 25, 2020, 5:07 PM HST (Updated November 25, 2020, 5:07 PM)
Recall this lava flow crisis from years ago: lava breaks out of the normal confines of the long-lived Puʻu ʻŌʻō eruption, with flows advancing relentlessly toward residential areas downslope. Over several months, the USGS Hawaiian Volcano Observatory and County of Hawai‘i Civil Defense Agency monitor the hazards closely in lower Puna as the situation evolves.
While this scenario describes the highly destructive 2018 eruption on the lower East Rift Zone (LERZ) of Kīlauea, it also pertains to an earlier event on the East Rift Zone: the Thanksgiving Eve Breakout (TEB) lava flow in 2007.
Although the TEB flow was much less destructive than the 2018 LERZ eruption, it nevertheless threatened homes in lower Puna for months. The TEB episode also bore important lessons on lava flow hazards that are worth considering in any future rift zone eruption in Hawai‘i.
By late 2007, the Puʻu ʻŌʻō eruption, on the middle East Rift Zone of Kīlauea Volcano, was already 24 years old and showed no signs of slowing down. A new vent had formed in July just east of Puʻu ʻŌʻō cone, with lava heading north of the rift zone, forming a large perched lava channel during September through November.
Early on Nov. 21, the day before Thanksgiving, lava broke out of the vent area on the south flank of the elevated lava channel, and the slope of the channel levees helped direct lava toward the south.
The new TEB flow slowly advanced downslope toward the south, with the pāhoehoe lava forming a lava tube as it moved. The flow cut through the remains of Royal Gardens subdivision on its course to the ocean.
The TEB flow reached the coastline, just west of Kalapana, in March 2008. Its lava tube remained active for three years, supplying lava to ocean entries (including the long-lived Waikupanaha entry). The consistent supply through the tube allowed the flow to gradually widen on the low slopes of the coastal plain.
In mid-2010, the eastward expansion of the flow began threatening Kalapana Gardens subdivision. The subdivision had been covered by lava flows in 1990, with subsequent rebuilding in later years. Between July 2010 and January 2011, a slow-motion lava flow crisis destroyed three homes, while threatening many more.
Eventually, a backup of magma in the system near Puʻu ʻŌʻō drove rising pressure, which then caused an intrusion and new vents to form west of Puʻu ʻŌʻō in March 2011. Within weeks, however, activity shifted back to Puʻu ʻŌʻō, and it continued with its eruptive activity from new vents for another seven years.
What can we learn from the TEB episode 13 years ago? The main takeaway is that a minor shift in vent position on the rift zone can cause a major change in lava flow direction and the resulting hazard.
When the TEB breakout started, it moved the vent location by just a stone’s throw, and yet it shifted the entire thrust of the flow from north to south. The precise location of a vent relative to the axis of the rift zone, which forms a subtle ridge, can determine which side of the ridge the flows descend. This was also a factor in why lava flows headed northeast during the 2014–2015 Pāhoa lava flow crisis.
The TEB flow also shows how an eruption can build new features on the rift zone, like lava channels and lava shields, that can influence subsequent flow direction. More recently, during the 2018 LERZ eruption, lava from early fissures built up new topography that contributed to the destructive fissure 8 flow focused northeast towards Kapoho subdivisions. The early lava kept the fissure 8 flow from moving southeast towards less populated areas.
These examples illustrate why the opening hours or days of a rift zone eruption are so consequential for hazards, both for Kīlauea and Mauna Loa. When an eruption starts, geologists must keep a close eye on the position of fissures relative to the rift zone axis. And they must be on the lookout for growing features like lava channels or shields that may shunt subsequent lava in a new direction.
The 2007 TEB episode of the Puʻu ʻŌʻō eruption, and rift zone events since then, are a reminder that big changes in hazards can hinge on small changes at the vent.
Volcano Activity Updates
Kīlauea Volcano is not erupting. Its USGS Volcano Alert level remains at NORMAL. Kīlauea updates are issued monthly.
Kīlauea monitoring data for the past month show variable but typical rates of seismicity and ground deformation, low rates of sulfur dioxide emissions, and only minor geologic changes since the end of eruptive activity in September 2018. The water lake at the bottom of Halema‘uma‘u continues to slowly expand and deepen. For the most current information on the lake, go online.
Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to an eruption from the current level of unrest is certain. Mauna Loa updates are issued weekly.
This past week, about 89 small-magnitude earthquakes were recorded beneath the upper-elevations of Mauna Loa. Most of these occurred at shallow depths of less than about five miles. Global Positioning System (GPS) measurements show long-term slowly increasing summit inflation, consistent with magma supply to the volcano’s shallow storage system. Gas concentrations and fumarole temperatures as measured at both Sulphur Cone and the summit remain stable. Webcams show no changes to the landscape. For more information on the current monitoring of Mauna Loa Volcano, go online.
There were two events with three or more felt reports in the Hawaiian Islands during the past week: an M2.3 earthquake 10 miles S of Volcano at a three-mile depth on Nov. 25 at 7:38 a.m. HST, and an M3.1 earthquake four miles ENE of Pāhala at a 19-mile depth on Nov. 21 at 6:26 a.m. HST.
HVO continues to closely monitor both Kīlauea and Mauna Loa for any signs of increased activity. Email questions to [email protected].