1 / 14

Can eruptions be forecast?

Can eruptions be forecast?. Chris Newhall, US Geological Survey Seattle. Principal methods of volcano monitoring (All on surface, in lieu of an internal gas pressure gauge! Most, looking for repeated patterns of precursory change).

huy
Download Presentation

Can eruptions be forecast?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Can eruptions be forecast? Chris Newhall, US Geological Survey Seattle

  2. Principal methods of volcano monitoring (All on surface, in lieu of an internal gas pressure gauge! Most, looking for repeated patterns of precursory change)

  3. For better, process-based forecasts, we need to track what makes volcanoes erupt... GAS!

  4. magma input from depth Gas leaks --> Lava domes Viscous magma + Slow ascent to surface --> preeruption gas leakage --> low explosive potential. H Mader/CN

  5. magma input from depth ‘Effusive’ eruptions. • low viscosity magma • --> gas highly mobile and can escape easily silicate melt + dissolved gases (H2O, CO2, S) (+ crystals) After H Mader

  6. Lava pond on Mauna Ulu (Hawaii) 1969 - bubble is ~ 5 metres across.

  7. magma input from depth Explosive eruptions. • high viscosity magma • --> gas not very mobile and cannot escape easily • IF ALSO rapid ascent, • --> high gas content persists to near surface • --> large potential expansion silicate melt + dissolved gases (H2O, CO2, S) (+ crystals?) After H Mader

  8. Two modes of conduit, eruptive behavior Open, Leaky Convection in the conduit, releasing most gas Closed, Tight No convection in the conduit(s); incoming gas is stored Infrequent, large explosive eruptions Frequent, sm eruptions (or no eruptions at all) Weak and/or short eruption precursors; warnings difficult Strong eruption precursors; ample warnings Popocatepetl (1994- ), Sakurajima, Mayon, Kilauea; Iwo-jima E.g., Pinatubo, Mount St. Helens

  9. Open vent: Sakurajima Volcano, Japan Explosions/day Earthquakes/day, < 1 km deep Earthquakes/day, 1-15 km deep (1987) K. Kamo et al.

  10. Take home message #1: Forecast success rates? ---------------------------------------------------- • Volcano restless, eruption possible? >95% • Eruption next few days? >50% Hours?<50% • Explosive potential? >95% • Actual explosive magnitude? Tough, maybe 50%

  11. Take home message #2: • Biggest uncertainty is the degree to which magma is still trapping gas as it nears the surface, i.e., how tight or leaky the volcano. • Gas content, pressure in magma cannot be measured directly. Gas monitoring is relatively rare; more often, we rely on proxies like seismicity and ground deformation.

  12. Take home message #3: • Big eruptions generally easier to forecast, with lead times of days to months. • The smallest, most frequent eruptions, are tough to forecast with useful lead times. • In all cases, eruption detection and tracking still critically needed!

  13. JB

More Related