Another view of the flow front in the northwest portion of Kaohe Homesteads. The leading portion of the flow front narrowed over the past two days and was roughly 150 m (500 ft) wide. Photo courtesy of USGS/HVO

http://youtu.be/8kOHXAaHCmo
Pu’u ‘O’o Crater East Rift Zone. (9/11-18/14)

http://youtu.be/QRcGXFuLsNI
Kilauea June 27th Lava Flow Time-Lapse, September 12-18, 2014

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

The USGS Hawaiian Volcano Observatory (HVO) and Hawai‘i County Civil Defense (HCCD) are working closely together to gather and share information about the June 27th lava flow through daily helicopter overflights. Currently, Darryl Oliveira (HCCD Administrator) flies early each morning to measure the flow’s advancement and direction and to assess fire and smoke conditions. These observations are compiled in a report available to the public later the same morning at http://www.hawaiicounty.gov/active-alerts/.

HVO overflights are scheduled 3-4 times per week to complement the County flights, with additional flights as necessary. During the HVO flights, geologists map the perimeter of the flow from the air, take photos, video, and infrared imagery, and assess eruptive conditions along the flow and at Puʻu ʻŌʻō. On at least one of these flights each week, we sample the lava to determine whether the chemistry of the lava is changing (it’s not).

We also try to measure the volume of lava being erupted by estimating the amount of lava flowing through the June 27th lava tube. This low-precision method suggests that between about 300,000 and 500,000 cubic meters (55,000–92,000 gallons per minute) of lava are being erupted each day, which spans the long-term average for the eruption as a whole (since 1983).

Based on feedback from the public, it’s clear that our maps are an important means of communicating information about the lava flow. Therefore, we’d like to offer some clarification of the information included in the maps. Each HVO map shows the current position of the June 27th lava flow relative to nearby structures. By comparing the current position with past flow positions, we estimate the flow’s current advance rate, which has varied over the past week.

An important feature now included on HVO’s maps is the calculated paths of steepest descent, shown as blue lines. These blue lines are not stream beds, but can be envisioned as the regional drainage pattern. In other words, they are the paths where any fluid, including lava, would be likely to flow.

In addition to thoroughly documenting the current position and advance rate of the flow, HVO scientists also recalculate the downslope paths from the newly mapped flow-front position to get the best sense of where the lava is headed. While the regional drainage pattern gives us a fairly good idea, it is based on a digital elevation model (DEM) that may have errors in it. With the new downslope path calculations, however, random variations of plus or minus 5 m (16 ft) elevation are added to the original DEM at random locations to see if, after thousands of runs, this “noise” significantly changes the downslope path.

The results from these secondary calculations do not differ significantly from the regional drainage pattern, but they do show us how some of the downslope paths can be connected in ways that may not be obvious in the regional map. This helps us to choose which one of the possible regional drainage lines is the preferred future lava-flow path. As part of the post-overflight maps, we now indicate that preferred path on a satellite image as a series of arrows that illustrate the next two weeks of time.

Based on the data we acquired during the overflight, HVO issues a forecast in the form of a Volcanic Activity Notice (VAN) that is posted on the HVO website along with the Kīlauea daily eruption update (http://hvo.wr.usgs.gov/activity/kilaueastatus.php). The VAN includes our best estimates of when the June 27th lava flow will reach significant infrastructures based on the flow’s current advance rate. You can sign up to receive VANs, which are distributed via the USGS Volcano Notification Service (VNS), by subscribing to VNS at http://volcanoes.usgs.gov/vns/.

HVO products – maps, photos, videos, updates and VANs – can all be accessed online at http://hvo.wr.usgs.gov/activity/kilaueastatus.php, or through links listed in the yellow box on our homepage (http://hvo.wr.usgs.gov).

Our products evolve in response to the needs and requests from partner agencies and the public. We have received a lot of feedback, both positive and negative, via our email address, askHVO@usgs.gov, and continue to welcome constructive comments and suggestions.

We also encourage Puna residents to stay informed about the June 27th lava flow. As stated in last week’s Volcano Watch article, while we are hoping for the best, we must also plan for the worst.