Geological monitoring involves frequent field visits to active vents and lava flows to observe and document newly created volcanic features and to sample lava or tephra for chemical and mineral analyses. Monitoring also includes analyses of images from aircraft, webcams, time-lapse cameras, and satellites, with automatic detection and alarming of significant changes.
Geologists require "boots on the ground" and "eyes in the sky" to observe volcanic eruptions and their impacts. Even with sophisticated volcano-monitoring networks, direct observations and measurements are essential to knowing what a volcano is doing and how the activity might impact people and infrastructure.
The most accurate, but also the most time-consuming, way to map a lava flow is to walk along its edges and record location "points" with a handheld Global Positioning System (GPS) device. Recording lava flow location points while flying in a helicopter can significantly shorten the time needed to map a flow, but is less accurate than mapping on the ground.
HVO geologists also collect oblique aerial photographs and infrared images of lava flows during helicopter missions, and then use computer software to stitch them together to form large mosaics. Maps from mosaics of infrared images provide remarkable "pictures" of the many surface breakouts on an active flow, which allows better analysis of current flow behavior, as well as recent history and future advance of the flow.
Effusion rate—the volume of lava erupted per unit time—is a fundamental parameter used to characterize the vigor of an eruption, but is very difficult to measure in real time. The most common way that geologists estimate effusion rate is to measure changes in a lava flow's surface area and thickness over a specified period of time. Area can usually be mapped relatively accurately, but flow thickness can vary by up to several meters (yards) across a flow. To account for this variability, geologists typically estimate an average thickness for the flow. Satellite or airborne radar technology can sometimes be used to more accurately calculate the volume of erupted lava.
Molten lava is conductive, so the shape of the electromagnetic field induced around an active lava tube can be measured. Using data from a handheld device that receives very-low-frequency (VLF) radio waves transmitted by the U.S. Navy for communications, geologists can calculate the cross-sectional area of molten lava within the tube. If the velocity of the lava stream can also be measured, such as with a radar gun through a nearby skylight (opening in the lava tube roof), then the effusion rate can be determined.
Effusion rate can also be estimated from the amount of sulfur dioxide (SO2) gas continuously emitted from an eruptive vent. This technique assumes that a fixed quantity of SO2 is emitted per unit of lava erupted at the surface. A typical current effusion rate for Kīlauea is 1–2 m3per second, equivalent to about 1-2 million gallons per hour.
It is not practical for geologists to continuously observe an eruption for long periods of time. Proliferation of digital cameras in recent years has enabled HVO to deploy on Kīlauea and Mauna Loa a network of webcams and time-lapse cameras that act as surrogate eyes. These cameras have recorded volcanic activity not directly or previously seen and have improved HVO's ability to interpret other monitoring data, such as seismicity and deformation. Webcams have significantly improved HVO's capability to characterize the current status of Kīlauea's ongoing eruptions and have enabled anyone with Internet access to observe Hawaiian volcanoes directly.Webcams can be viewed within our Multimedia section, and a selection of time lapse movies of the East Rifr Zone eruption of Kīlauea Volcano was published in 2008.
Magmas with subtly different chemistries are supplied from the Hawaiian hot spot to the summit reservoirs of Hawaii's active volcanoes at intervals of months to years. These magmas can then erupt from or be stored in underground magma reservoirs within the volcano. The chemistry of erupted lava and tephra (airborne fragments of lava) is used as a fingerprint to track the progress of magma as it is transported from summit reservoirs through rift zone plumbing systems. For these reasons, HVO geologists regularly collect samples of lava and tephra to conduct detailed studies of their physical characteristics, the types and abundance of minerals they contain, and their chemistries.