1. A global perspective on volcanoes and eruptions Richard Wunderman, Lee Siebert, James Luhr, Tom Simkin, and Ed Venzke Smithsonian Institution National Museum of Natural History Global Volcanism Program Washington, D.C.

2. Overview of talk The Smithsonian’s involvement Terminology, geography, and where explosive volcanoes reside Patterns and trends Conclusions

3. 1968-75Center for Short-Lived Phenomena 1975-89Scientific Event Alert Network Bulletin (SEAN Bulletin) 1990-Bulletin of the Global Volcanism Network (GVN Bulletin) 1996- Website of Global Volcanism Program 2000-Weekly Reports (with USGS) YearsPublication Names

4. Global Volcanism Program Databases covering the past 10,000 years (the ‘Holocene’) including ~1500 volcanoes, their ~8900 eruptions, and over 21,000 images. On-going eruptive activity discussed in both the Bulletin of the Global Volcanism Network (monthly) and Weekly Reports. Website. Databases covering the past 10,000 years (the ‘Holocene’) including ~1500 volcanoes, their ~8900 eruptions, and over 21,000 images. On-going eruptive activity discussed in both the Bulletin of the Global Volcanism Network (monthly) and Weekly Reports. Website.

5. Aerial shot of Grímsvötn eruption plume,18 December 1998. Courtesy of NVI; photo by Karl Grönvold (GVN Bull 23:11). Ash plume reached ~10 km altitude.

8. Subduction

9. Ocean Sea floor basalt and mud Upper mantle Over-riding plate (SiO 2 enriched) Subducting slab Shallow seas (or continental margin) Subducted seawater (blue) rises into the overlying mantle where it triggers partial melting. Pods of melt ascend (yellow).

10. Subduction-related volcanism Chains of volcanoes producing volatile- rich (wet) magmas that can erupt violently (lava domes, caldera eruptions, many landscape-altering eruptions with tall ash plumes) In USGS aircraft-ash encounter database these volcanoes were the source for vast majority of incidents

11. Terminology A general term for fragmental material ejected during an eruption is tephra; the fine-grained partition is ash (diameter  2 mm) Study of tephra layers enabled dating of many pre-historic Holocene eruptions, now tabulated in our data base Eruption–solid volcanic products or molten magma must arrive at the surface USGS photo

13. Some eruptions are hard to miss... Still evaluating ways to estimate their size and impact. It can take years to evaluate an eruption using conventional methods. More than half the world’s known active volcanoes found in developing nations. USGS photo

14. How many volcanoes active? Deep marine volcanism nearly absent from our database Our definition of ‘volcano’ tends to lump vents with spatial and geochemical affinity together into groups or fields, which are counted as a single volcano ‘Active’ means erupted in the past 10,000 years (‘the Holocene’), but large volcanoes are capable of erupting after longer repose intervals

15. How many volcanoes active? Holocene~ 1300—1500 Holocene, subduction~ 1100 Historically documented~ 560 Annually, in past few decades~ 50—60 Historical, nearly continous 10-15

16. VEI: An attempt to quantify qualitative data Newhall and Self (1982)

17. Large eruptions: How many? VEI  3VEI  4 Holocene~1440 ~490 Tephra studies, excluding historical records ~460 ~280 In historical records ~970 ~210

18. Interval from start to climax (paroxysm):  1 hour (~20%)  1 day (~40%)  1 week (~50%)... but can extend to over 20 years

19. Eruption duration

20. How many ash clouds to cruising altitudes (10 km, 33000 ft)? During the decade 1975-85, GVN Bulletin reports and Simkin (1991, USGS Bull 2047) noted ~60 clouds Probably missed some eruptions Altitudes of plume top—poorly constrained Often very hard to say how an eruption will progress Not a good idea to fly over a tall plume

21. GVP website www.volcano.si.edu