VOLCANO WATCH: Satellites

As part of Volcano Awareness Month, Hawaiian Volcano Observatory’s January Volcano Watch articles are addressing how the USGS HVO responds to threatening lava flows.  This week, the focus is on the use of satellite data to track lava flow activity.

Although satellites were in orbit and transmitting images of Earth’s surface in 1990, when the Kalapana community was inundated by lava, their data were not used to map lava flows.  Without the Internet, satellite imagery could be distributed only by copying the data onto tapes that then had to be mailed.  This process could take weeks, so the images were typically not used to help monitor a rapidly evolving crisis.  In addition, computers in 1990 were not fast enough and did not have enough memory to work with large satellite datasets.  Loading and viewing an individual image could take hours!

Instead of satellite imagery, HVO relied upon high-altitude aerial photos for occasional broad views of the Kalapana lava flow field in 1990.  Some of these photos were taken by HVO scientists who aimed cameras through holes cut in the bottom of Hilo-based airplanes, while others were taken by a private Honolulu-based company that specialized in aerial photography.  The photographs then had to be developed, printed, and delivered to HVO—a process that required a few days.  The information was therefore largely outdated by the time HVO received it, but the aerial photos formed an important base for ground-based mapping (the topic of next week’s article).

With today’s Internet, it’s now possible to obtain timely satellite data about the June 27 lava flow within hours of image acquisition.  Modern computers can also process massive amounts of data rapidly, enabling scientists to fully exploit the multitude of satellites that are now orbiting and imaging Earth.

Thermal images, which show the temperature of Earth’s surface, are perhaps the most obvious type of satellite data used to monitor lava flows.  Thermal data allow HVO scientists to identify hot areas that correspond to breakouts of lava on the flow field.  These data can be used to determine the lava eruption rate—a key monitoring parameter—by assuming that the temperature of the lava flow field is related to the amount of lava on the surface.

Visual data—essentially photographs from space—are also available from satellites.  Many of these data have exceptionally high resolution and are capable of discerning objects less than a meter (yard) in size, which helps HVO scientists make detailed maps of the lava flow and document changes over time.

Thermal and visual satellite data, however, both suffer from a major weakness: clouds.   As most Hawaiʻi residents know, Puna is frequently covered by clouds, which obscure the view from space.  Fortunately, there is one form of satellite imagery that can see through cloud cover—radar!

Whereas visual and thermal satellite images are essentially photographs that rely upon light or temperature generated by, or reflected from, Earth’s surface, radar provides its own energy.  Radar satellites transmit a pulse of energy to the surface and then measure the strength of the reflected energy, much like a flash camera.  These radar signals can “see” through clouds, and lava flows are easily distinguished from the surrounding forest based on their strong reflection.  Unfortunately, it is difficult to distinguish active from inactive lava flows in radar images.

HVO, therefore, uses an array of complementary satellite tools to monitor the June 27 lava flow—thermal, visual, and radar.  Because satellite data are easily shared via the Internet, the images can be viewed from anywhere.  In fact, USGS scientists across the country—from Virginia to Alaska—assist HVO by examining satellite data of the Puna lava flow field and sharing their results and interpretations with HVO scientists.

Some of these data, especially those provided by NASA, are accessible via public websites, so anyone with access to the Internet can examine satellite images of lower Puna.

Next week, we will look at ground-based and airborne methods used to track lava flows. In the meantime, we encourage you to check out the schedule of upcoming Volcano Awareness Month talks posted on HVO’s website.

Kīlauea activity update

Kīlauea’s East Rift Zone lava flow remained active with breakouts scattered across the leading 3 km (2 miles) of the flow, in the area near the abandoned True/Mid-Pacific geothermal well site, and farther upslope near Puʻu ʻŌʻō. Among these breakouts, the most significant was a lobe that branched off from the north edge of the flow about 1.5 km (0.9 mi) upslope from Highway 130. This flow lobe was about 1 km (0.6 mi) from Highway 130 on Thursday, Jan. 15, according to Hawaiʻi County Civil Defense.

The summit lava lake rose slightly over the past week, and was about 44 meters (144 ft) below the rim of the Overlook crater on Thursday morning.

Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey`s Hawaiian Volcano Observatory.