A global perspective on volcanoes and eruptions

Richard Wunderman, Lee Siebert,

James Luhr, Tom Simkin, and Ed Venzke

Smithsonian InstitutionNational Museum of Natural HistoryGlobal Volcanism Program Washington, D.C.

Overview of talk

• The Smithsonian’s involvement

• Terminology, geography, and where explosive volcanoes reside

• Patterns and trends

• Conclusions

1968-75 Center for Short-Lived Phenomena

1975-89 Scientific 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)

Years Publication Names

Global Volcanism ProgramGlobal 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.

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.

Subduction

Ocean

Sea floor basalt and mud

Upper mantle

Over-riding plate (SiO2 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).

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

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

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

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

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

VEI: An attempt to quantify qualitative data

Newhall and Self (1982)

Large eruptions:How many?

VEI 3 VEI 4Holocene ~1440 ~490

Tephra studies, excluding historical records

~460 ~280

In historical records ~970 ~210

Interval from start to climax (paroxysm):

1 hour (~20%)

1 day (~40%)

1 week (~50%)

. . . but can extend to over 20 years

Eruption duration

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

GVP website www.volcano.si.edu