The USGS Hawaiian Volcano Observatory has released a new map charting the cumulative thickness of tephra erupted at Kīlauea’s summit, built from a helicopter lidar survey flown July 29, 2026. The map, published September 3, shows the tephra cone on the western rim of Halemaʻumaʻu crater has reached 1,186 meters (3,891 feet) above sea level — a cumulative thickness of 47 meters (154 feet) measured against pre-eruption ground level.
The survey followed the end of lava fountaining episode 52, capturing the crater floor and tephra deposit before two subsequent episodes (53 and 54) altered the terrain. HVO notes those later episodes did not substantially change the topography, so the map’s thickness values are still considered representative as of release.
Why Lidar Succeeded Where Photogrammetry Failed
What makes this a lidar story rather than just a volcanology one is the method HVO used to get there. The Observatory has historically relied on photogrammetry to model topography at the summit, but that approach has failed to capture the tephra deposit accurately. Two problems compound each other: the deposit’s surface is largely featureless, denying photogrammetry the visual texture it needs to build a model, and the eruption’s persistent gas plume obscures the area from optical sensors entirely.
Lidar sidesteps both issues. It can scan through cloud cover and volcanic gas, and it returns usable data from nearly any surface texture, featureless or not. HVO’s caption language is direct about the tradeoff: lidar data is harder to collect and process than photogrammetry, which is why these surveys happen less frequently — but for a target like an active tephra cone wrapped in its own gas plume, it’s the only method that reliably works.
Reading the Map
The resulting map is presented in two panels, both using the July 29 digital elevation model as a semi-transparent basemap. The left panel uses a narrow color band capped at 5 meters (16.4 feet), which is tuned to show the distal tephra deposit as it thins out into the Kaʻū Desert within Hawaiʻi Volcanoes National Park. The right panel zooms into the cone itself, with the color scale extended to 45 meters and beyond, to represent the full range of thickness at the accumulation’s core.
This is a helicopter-based survey, distinct from the fixed-wing and drone lidar platforms that dominate most commercial and infrastructure mapping coverage — worth noting for readers who associate lidar primarily with terrestrial or UAV applications. Helicopter deployment makes sense here given the terrain: an active eruption site with an unstable, gas-obscured surface isn’t a candidate for ground-based scanning or safe low-altitude drone work, and fixed-wing platforms lack the maneuverability to work tightly around a crater rim.
An Ongoing, Shifting Eruption
Kīlauea’s episodic lava fountaining eruption has been ongoing since December 2024, and the tephra accumulation has been substantial enough to bury infrastructure — the story includes an image of HVO staff digging out a volcanic gas monitoring station that was buried by the deposit. As of the report, the summit was inflating again at a steady rate, with the next fountaining episode forecast within the week, meaning this map represents a snapshot that will likely need updating again before long.
Why It Matters
This is a clean example of lidar’s advantage over photogrammetry in a specific, hard-condition environment — persistent obscurant (gas), zero surface texture, and a monitoring need that’s directly tied to public safety within a national park. It’s also a good illustration of survey cadence tradeoffs: HVO’s own language acknowledges they don’t fly lidar as often as they’d like because of the collection and processing burden, even when it’s clearly the superior tool for the job.
Source: Big Island Video News, September 6, 2026 — https://www.bigislandvideonews.com/2026/09/06/new-map-shows-erupted-tephra-thickness-at-kilauea-summit/
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