In mapping and geographical analyzes of volcanoes, especially in Hawaii, there is perhaps nothing more important than having an accurate numerical model of topography. These models depict the three-dimensional nature of the Earth, clarify features from past eruptions and influence potential pathways for future activity.
But how are these forms created?
Modeling the terrain on active volcanoes is different from anywhere else because dramatic changes can occur on timescales much shorter than a human lifespan. For example, in 2018 in Kilauea, approximately 1 km of rock volume (0.25 cubic miles) was lost at the summit of the volcano and deposited in the Lower East Rift Zone.
Therefore, topographic models can become outdated relatively quickly, and we need to update them accordingly.
Due to the vastness of the areas to be designed, measuring altitudes on the ground with GPS is not possible, except for verification of other measurement techniques. Therefore, remote sensing is preferred – measuring the features of the Earth from the air.
For many decades, aerial photography was the preferred remote sensing technique used by the United States Geological Survey to model the terrain. Interlaced aerial images taken from slightly different positions along the flight line can be projected to make the observer believe they are seeing a 3D scene rather than 2D images, similar to how the human eyes sense depth. Using a large and complex tool called a hologram, the user can draw the outlines of lava flows and lines of equal height, or contour lines, in such an expected scene.
Aerial photography began to decline towards the end of the twentieth century with the advent of new technologies. As such, the last aerial photography surveys to cover the entire island of Hawaii were completed in the early 1980s. Years later, the data was compiled into a digital island elevation model with a resolution of 10 meters (yards), which is still used today.
However, Kilauea does not always cooperate with geographers’ desire to maintain current topographic data.
When the eruption of Pu’u ‘O’o volcano began on January 3, 1983, it marked the start of 35 years of near-continuous topographical changes at Kilauea that reached their peak in 2018. Some reasonably successful remote sensing operations occurred during this time, most of them Especially a survey conducted by the National Oceanic and Atmospheric Administration in 2005, but with the continued explosion, some data is bound to instantly become obsolete.
In the months following the 2018 eruption, it became apparent that a pause in volcanic activity might be an opportunity to finally update Kilauea’s topography. Accordingly, the LiDAR survey is planned and completed in July 2019.
LiDAR stands for ‘Light Detection and Range Detection’ – the laser pulse instrument was transported over the landscape on board a helicopter, with a sensor measuring return times of each light pulse depending on the distance from the device to the target.
The primary data set resulting from the LiDAR scan is a “point cloud”. All objects reflecting a light wave are photographed, including vegetation, structures, and land. Often “first returns” in forested areas depict the canopy of a tree, and sometimes this data is useful to ecologists, but geologists are more concerned with the last returns or “bare earth”.
To create a useful DEM from a point cloud, a filter is applied to exclude all points except for abstract ground points, and then height values are calculated from points for each cell in the grid – most often by averaging. The DEM from Kilauea LiDAR 2019 (https://doi.org/10.5066/P9F1ZU8O) has 1 meter (3.28 feet) grid cells with calculated heights that should be accurate to 10 centimeters (4 inches). Data was verified by comparison with GPS ground control points surveyed in Spring 2019.
With a reliable topographic model available for Kilauea now, the USGS Hawaiian Volcano Observatory can combine this data with existing models that still reliably depict other areas to create a new 3D model for each island of Hawaii. The dataset is used by Hawaii Volcanoes National Park and the County of Hawaii; It will be combined into various maps, enabling more accurate projections of lava flow directions from future eruptions.
This dataset will be up to date until the moment the lava erupts again, and the entire process will likely repeat itself. Hawaiian volcanoes have a way to keep geologists and geographers on their toes!
Volcano activity updates
Kilauea volcano does not erupt. The USGS Volcano Alert Level remains at Normal (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kilauea updates are released monthly.
Kilauea monitoring data for last month show variable but typical rates of earthquakes and ground deformation, low rates of sulfur dioxide emissions and only minor geological changes since the end of volcanic activity in September 2018. The lake of water at the bottom of Halema’uma ‘continues to expand and deepen slowly. For the most recent information about the lake, visit www.usgs.gov/volcanoes/kilauea/k-lauea-summit-water-resources.
Mauna Loa does not erupt and is still in the Volcano Alert Level Alert. This alert level does not imply that an eruption is imminent or that progression to an outbreak from the current level of unrest is certain. Mauna Loa updates are released weekly.
Last week, about 31 small-scale earthquakes were recorded under the upper elevations of Mauna Loa; Most of them occurred at shallow depths of less than 8 km (about 5 miles). GPS measurements show a slow rise in long-term summit magnification, consistent with the supply of magma to the volcano’s shallow storage system.
Gas concentrations and fumarol temperatures as measured in the sulfur cone and summit remain stable. Web cameras do not show any changes to the landscape.
For more information on the current monitoring of Mauna Loa volcano, visit www.usgs.gov/volcanoes/mauna-loa/monitoring.
There have been five events with three or more hairy reports on the Hawaiian Islands over the past week: M3.0 22 km (13 mi) earthquake ENE from Honaunau-Napo’opo’o at a depth of 2 km (1 mi) at 8:21 a.m. 18 November, M3.0 9 km (5 mi) earthquake ENE from Pahala at a depth of 31 km (19 mi) at 3:31 am November 16, the M2.9 earthquake 12 km (7 mi) southeast of the fern forest at a depth of 7 km ( 4 mi) at 9:18 pm November 15, M3.0 11 km (6 mi) earthquake southeast of Verne Forest at a depth of 7 km (4 mi) at 3:21 pm November 15, M3.8 earthquake 12 km ( 7 mi) ESE from Waimea at a depth of 6 km (3 mi) at 9:36 am on Nov.13.
HVO continues to monitor Kilauea and Mauna Loa closely for any signs of increased activity.
Visit the HVO website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, and more. Email questions to [email protected]
Volcano Watch is a weekly article and activity update written by the scientists and affiliates of the US Geological Survey’s Hawaiian Volcano Observatory.
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