Volcanic Hazards Primary Effects -lava flows -pyroclastic eruptions -poisonous gas emissions Secondary Effects -mudflows and debris avalanches -flooding (glacial outburst floods) -tsunamis -seismicity -atmospheric effects and climate change Volcanic Hazards along the Cascadia Subduction Zone Predicting Eruptions Monitoring the Movement of Magma -seismic studies -magnetic field changes -electrical resistivity Physical Anomalies and Precursor Phenomena -ground deformation -change in heat output
Transcript
Volcanic HazardsPrimary Effects-lava flows-pyroclastic eruptions-poisonous gas emissions
Secondary Effects-mudflows and debris avalanches-flooding (glacial outburst floods)-tsunamis-seismicity-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting EruptionsMonitoring the Movement of Magma -seismic studies -magnetic field changes-electrical resistivity
Physical Anomalies and Precursor Phenomena-ground deformation-change in heat output-change in the composition of gases-local seismic activity
Basaltic eruptions are very fluid and will flow great distances from the vent or rift. The photo above is taken from the Kilauea rift zone on the Big Island of Hawaii.
Pahoehoe Flow, Hawaii
Aa Flow, Hawaii
Few fatalities are typically associated with basaltic lava eruptions, as neighborhoods, such as the one shown here, can be evacuated. Buildings and other human-made structures are not so lucky!
Basaltic lava flow reaching a neighborhood near Kilauea, Hawaii.
Lava flow induced fire, Hawaii.
Pyroclastic eruptions and flows produce some of most devastating effects associated with volcanism. Destruction is total to any living organism or structure within the pathway of a pyroclastic flow.
Landslide north face of Mt. St. Helens May 18, 1980.
Mt. St. Helens May 18, 1980
Mount St. Helens: Pyroclastic flow May 18, 1980.
Bishop ash was erupted catastrophically 760,000 years ago in eastern California. The eruption had a VEI = 7 and ashfall accumulated as far Nebraska.
Pompeii, Italy 79AD
Volcanic HazardsPrimary Effects-lava flows-pyroclastic eruptions-poisonous gas emissions
Secondary Effects-mudflows and debris avalanches-flooding (glacial outburst floods)-tsunamis-seismicity-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting EruptionsMonitoring the Movement of Magma -seismic studies -magnetic field changes-electrical resistivity
Physical Anomalies and Precursor Phenomena-ground deformation-change in heat output-change in the composition of gases-local seismic activity
Causal Factors for Lahar Flows
Lahar flow from Mt. Pinotubo.
Volcanic tephras are well-preserved in lacustrine and bog sediment throughout the Cascades. Ubiquitous organic matter provides excellent opportunities to assign radiocarbon ages to the eruptions.
The Mt. Mazam O (Crater Lake) eruption occurred ~6800 years ago.
Excavating a trench behind the Hyak moraine at Snoqualmie Pass (ca. 1990).
Three tephra layers are presnt in the sediment record at Snoqualmie Pass. They have been independently dated using radiocarbon dating of associated organics.
Mt. St. Helens Wn
Mt. St. Helens Yn
Mazama O
Tephra distribution from Mt. Mazama, Longvalley and Yellowstone eruptions.
Tephra distribution of Cascade volcanoes
Isopachs of Glacier Peak tephra distribution (13,100 yr BP).
Isopachs of Glacier Peak tephra distribution (13,100 yr BP).
Following a large edifice collapse ~5000 years ago the mountain lost ~1500 feet of its summit.
Mt. Rainier’s glacial ice is a major potential source
Mt. Rainier contain 90% of the Cascade’s glacial ice and permanent snow.
Oceola Lahar (~5200 yr BP) near Enumclaw, WA.
Glacier Peak has been active Cascade volcano over the past 15,000 years.
Unconsolidated pyroclastic deposits on north face of Mt. St. Helens source of lahar flows.
Reworked pyroclastics incorporated into Mt. St. Helens lahar deposits.
Volcanic HazardsPrimary Effects-lava flows-pyroclastic eruptions-poisonous gas emissions
Secondary Effects-mudflows and debris avalanches-flooding (glacial outburst floods)-tsunamis-seismicity-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting EruptionsMonitoring the Movement of Magma -seismic studies -magnetic field changes-electrical resistivity
Physical Anomalies and Precursor Phenomena-ground deformation-change in heat output-change in the composition of gases-local seismic activity
Can we predict volcanic eruptions?
Yes, but with caveats!!!
1.Requires a thorough understanding of the volcano’s eruptive history.
2.Requires appropriate instrumentation on the volcano well in advance of the eruption.
3.Requires constant monitoring of instrumentation so that incoming data can be properly interpreted.
The science behind predicting volcanoes has improved substantially over the past decades, but volcanologists can only provide probabilities regarding the timing of a given eruption. It is not possible to determine the exact severity of an eruption or whether the magma will even reach the surface.
How do volcanoloists predict volcanic eruptions?
1.Monitor seismic data related to movement of magma.
2.Monitor ground deformation and dome expansion.
3.Monitor volcanic gases emitted as magma rises and expanding gases are released.
Successful Volcanic Predictions:
Volcanologists predicted the eminencne 1980 Mt. St. Helens eruption. Their warnings of an impending blow prompted the U.S. Forest Service to evacuate people from dangerous areas near the volcano. Although 57 people died in the eruption, it is estimated that as many as 20,000 lives were saved.
In the spring of 1991, a USGS “SWAT team” was rushed to the Philippines' Mt. Pinatubo and successfully predicted the June eruption, leading to evacuations that saved thousands if not tens of thousands of lives and millions of dollars worth of military equipment at the nearby Clark Air Force Base.
