# Presentation: 201400

## 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.

**Notes:**
Hello I am RW; I edit the Bull of the GVN, the Smithsonian’s monthly summary of volcanism.

## Overview of talk

-  The Smithsonian’s involvement
-  Terminology, geography, and where 	explosive volcanoes reside
-  Patterns and trends
-  Conclusions

**Notes:**
After explaining a bit more about the SI, I will help clarify some terminology.  I do that in hopes that I can help bridge the gap between the varied disciplines represented here.  The patterns and trends portion of this talk mainly comes from previous written journal articles and books, largely by TS, LM, and LS.  One important conclusion is that ash probably gets to commercial aircraft cruising altitudes at least about once every two months on average.

## 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)

- 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**_

**Notes:**
The GVPs roots connect to earliest pubs that discussed such diverse topics as meteorites entering the atmos, lemming migrations, whale strandings, oil spills; info was sent to readers via postcards.

The last three dates represent ongoing publications and outreach efforts.  

## 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.

**Notes:**
Although we have only a small staff and rely heavily on freely submitted reports, we have succeeded in building an important resource on active volanoes. WRT the aviation-ash issue, our website provides outreach on a 24-7 basis that substitutes for our limited hours of operation.

## 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.

**Notes:**
Volcanism takes diverse forms and occurs in many environments.  Here’s an eruption that disrupted air traffic. It occurred in Iceland, a place where oceanic ridge emerges from the N Atlantic.  The eruption also began beneath a continntal glacier, ultimately melting through hundreds of meters of ice to punch its way to the surface.  The eruption reached reported altitudes of ~10 km.

## Slide 6

**Notes:**
Here’s a map of the globe showing the distrib of know volcanoes (red triangles) and oceanic ridges (red lines).  At the ridges we know volcanoes occur, but water depths prevent most observations.  The floor of the ocean is less known and imaged than the back side of the moon, presenting a scientific frontier but this emersion beneath seawater also means that they offer little risk to aviation.  The red triangles often occur in chains and elongate clusters, which bleed together at the scale of this map.  

The map also illustrates Earth’s tectonic plates, contrasting known volcanoes along plate margins and intraplate settings. Intraplate volanoes, such as the Hawaiian and Canary islands, typically erupt lavas in a comparably passive manner, and thus like the volcanism at depth along the ridges, present lesser hazards to aviation.   The example I just showed, Grimsaten volcano in Iceland, was along a ridge, but at a place where it emerges from the sea.  The abundance of water from the subglacial setting may have contributed to the explosive character of that rather anomalous ridge volcanism.

The ocean ridges (again, the red lines) are where new crust is created, the so-called divergent plate boundaries.  Conversely, the yellow lines show where the crust is consumed, the so-called convergent plate boundaries.  The process of consumng the crust is called Subduction and we often refer to volcanoes along those areas as subduct volc.  Notice that where volcanoes lie near population centers, they kind of volcano they lie near is often a subduction volcano.  As a broad rule these are the most dangerous and most likely to erupt and produce large plumes.

## Slide 7

**Notes:**
This pie chart shows the relative numbers of historic eruptions in our database WRT tectonic settings.  As I eluded to before, it is heavily biased towards volcanoes that have atmos impact, omitting deep ocean volcanism, which probably erupts a larger bulk of material but which we don’t see.

**Subduction**

**Notes:**

Subduction takes place along convergent margins

Marked by ocean trenches, earthquakes, and volcanoes with explosive eruptions 

Downward displacement of a lithospheric plate into the mantle beneath an overriding plate. 

## Over-riding plate (SiO2 enriched) 

- 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).

**Notes:**
Sea floor basalts and other rocks in the down going slab are rich in sea water.  Escaping water helps the surrounding rocks melt and have a low enough viscosity to rise to the surface to erupt as subduction volcanoes.  The volatiles in this setting can drive explosive eruptions.

## 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

**Notes:**
 Frothy, sponge-like particles (~ 0.1 mm across)
Bubble walls form small glassy particles with lots of surface area; nucleation sites for water, ice, condensates
 Holocene = last 10,000 yrs
 As we define it, the term ‘Eruption’ signifies . . . .

## Slide 12

## 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

**Notes:**
I DON’T LIKE THIS—BETTER TO SKIP THE FOLLOWING: The point is, most important eruptions will probably lack consistent, well-constrained information at the time scale of value to aviators.  It may prove worthwhile to look at previous cases, or similar cases in the literature or on our website. 

## 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)

**Notes:**
The Volc. Exp. Index is a useful scale, but most volcanologists realize that the fundimental data used to compile the VEI are vague, meaning that the VEI values are seldom very accurate or precise. In other words, for an eruption, neither the eruptive volume nor the ash cloud height are particularly well constrained parameters.  The VEI should not be confused with seismic magnitudes or Richter scale, which stem from instrumental measurements available shortly after an earthquake. Still, it’s a handy scale for looking at our eruptive data.

## Large eruptions:How many?

|  | VEI  3 | VEI  4 |
| --- | --- | --- |
| Holocene | ~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

** ****GVP website**              www.volcano.si.edu