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Surface temperatures reflect the temperatures below ground
Some volcanoes have particular thermal characteristics
Some volcanoes have thermal features such as smoking vents, geysers, hot springs, lava flows or lava domes. Surface temperature changes at these thermal features sometimes occur before a volcanic eruption. Recognition of these “thermal anomalies” can be useful in predicting changes in activity.
Several thermal features are worth noting
- Steam, or vapor-dominated features such as gas vents, fumaroles, and mud pots range in temperature from boiling up to several hundred degrees (about 400 °C or 750 °F).
- Water-dominated features include geysers, hot springs/pools, crater lakes, elevated sea surface temperature (e.g., from underwater or island volcanic activity), and even melting ice (e.g., sub-glacial volcanoes). These range in temperature from freezing to boiling.
- Lava-dominated features include lava lakes, lava flows, lava domes, and pyroclastic flows, and can reach temperatures up to about 1200 °C (2200 °F).
Norris-2003. a YVO scientist takes a temperature measurement at “Son of Green Dragon” thermal feature.
Ground temperature measurements are important for the complete study of the evolution of a volcano
Directly measuring the temperature of hot spring basins, fumarole fields, or active lava flows can be dangerous. For very precise measurements, scientists place devices called thermocouples directly onto the hot surface of a thermal feature. Such measurements are most often made at volcanoes that are easily accessible, and scientists only conduct the measurements if the areas are safe to be in for several minutes. Although direct measurements are very precise, they are limiting because they can only cover a small or specific area.
Temperature measurements can also be made remotely using cameras or instruments that measure thermal infrared radiation, which is emitted from the heated surface. However, TIR radiation can be partially or completely obscured by thick clouds or ash plumes, so these types of measurements must be made under favourable atmospheric conditions. A common instrument used by scientists in the Volcanic Hazards Programme is a front-facing (thermal) infrared camera, which produces an image using a colour spectrum that correlates with the detected temperature.
This image shows an HVO geologist sampling the lava that was seeping out of the interior of the rootless shield. The lava was placed in a bucket of water to quench the sample. The top frame is a normal photograph, while the bottom frame is a thermal image taken within a fraction of a second of the photograph. As the thermal image shows, the incandescent interior of the flow, which is exposed as lava clinker spalls off, exceeds 1000 degrees Celsius (1800 degrees Fahrenheit). The geologist is shielding his face from the radiant heat.
Satellites can detect the thermal characteristics of volcanoes
This is an important tool for monitoring remote volcanoes with few ground facilities. Some satellite sensors make daily or semi-daily observations over volcanoes, but these sensors record images of large areas with low resolution, which limits the small-scale detail that can be seen of thermal features. More detailed, higher resolution TIR images can be obtained from satellite and airborne sensors, but observations are generally less frequent.
Composite satellite image of Veniaminof Volcano (Alaska) collected by Landsat-8 with short-wave infrared data to show thermal emissions from the active lava flow overlain onto a visible wavelength image. An eruption began in June, 2013 with lava effusion and ash emission, followed by a lull in activity. The active lava flow is shown in shades of yellow and orange, and extends southward from the vent. Thin deposits of volcanic ash are seen on the snow and ice, as radial spokes that form when ash is emitted under changing wind direction.
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