Fogo

by Casey Davidow
 

National Volcano Early Warning System

(NVEWS)

 I got the following information about NVEWS and the tables from the National Volcano Early Warning System published by the USGS. ² This graph assesses the threat posed by Fogo based on a number of criteria and then is used to decide whether or not Fogo is being well monitored.

 

Hazard and exposure factors used in threat assessment of U.S. volcanoes for the National Volcano Early Warning System.  

 

Hazards Factors

 

Score

Volcano type

If volcano type is cinder cone, basaltic field, small shield, or fissure vents: Score = 0

If volcano type is stratocone, lava domes, complex volcano, maar or caldera: Score = 1

1

Maximum Volcano Explosivity Index (VEI)

If maximum known VEI ≤ 2: Score = 0

If maximum known VEI = 3 or 4: Score = 1

If maximum known VEI = 5 or 6: Score = 2

If maximum known VEI ≥ 7: Score = 3

If no maximum VEI is listed by GVP and if volcano type = 0: Score = 0

If no maximum VEI is listed by GVP but volcano type = 1: Score = 1

If no known Holocene eruptions and the volcano is not a silicic caldera system: Score = 0

0

Explosive activity

If explosive activity (VEI ≥ 3) within the last 500 years: Score = 1

0

Major explosive activity

If major explosive activity (VEI ≥ 4) within last 5000 years: Score = 1

0

Eruption recurrence

If eruption interval is 1-99 years: Score = 4

If eruption interval is 100 – 1,000 years: Score = 3

If eruption interval is 1,000 to several thousand years: Score =2

If eruption interval is 5,000-10,000 years, or if no Holocene eruptions but it is a large-volume restless silicic system that has erupted in the last 100,000 years: Score = 1

If no known Holocene eruption: Score = 0

4

Holocene pyroclastic flows?

If yes: Score = 1

0

Holocene lava flows?

If Holocene lava flows have traveled beyond the immediate eruption site or flanks and reached populated areas: Score =1

1

Holocene lahars?

If Holocene lahars have traveled beyond the flanks and reached populated areas: Score =1

0

Holocene tsunami(s)?

Has it produced a tsunami within the Holocene? If yes: Score = 1

0

Hydrothermal explosion potential?

If the volcano has had Holocene phreatic explosive activity, and/or the volcano has thermal features that are extensive enough to pose a potential for explosive activity: Score =1

1

Sector collapse potential?

If the volcano has produced a sector collapse in Quaternary-Holocene time and has re-built its edifice, or, has high relief, steep flanks and demonstrated or inferred alteration: Score = 1

1

Primary lahar source?

If volcano has a source of permanent water/ice on edifice, water volume > 106 m3: Score = 1

0
     

Historical Unrest Factors

Score

Observed seismic unrest

Since the last eruption, in the absence of eruptive activity, within 20 km of the volcanic edifice? If yes: Score = 1

0

Observed ground deformation

Since the last eruption, in the absence of eruptive activity, inflation or other evidence of magma injection? If yes: Score = 1

0

Observed fumarolic or magmatic degassing

Since the last eruption, in the absence of eruptive activity, either heat source or magmatic gases? If yes: Score = 1

0

Total of Hazard Factors

8

Exposure Factors

 

Log10 of Volcano Population Index (VPI) at 30 km

Calculated with LandScan population database. Visitor statistics for volcanoes in National Parks and other destination recreation areas are added to the VPI factor where available.

 3.70

Log10 of approximate population downstream or downslope

Population outside the 30 km VPI circle included within the extent of Holocene flow deposits or reasonable inundation modeling. This factor to be used only with volcanoes that have a primary lahar hazard (e.g. Cascade stratovolcanoes) or significant lava flow hazard (e.g. Mauna Loa).

4.60

Historical fatalities?

If yes, and a permanent population is still present: Score = 1

0

Historical evacuations?

If yes, and a permanent population is still present: Score = 1

1

Local aviation exposure

If any type volcano is within 50 km of a jet-service airport, score = 1; if a Type 1 volcano is within 300 km of a jet-service airport, score = 1; if a Type 1 volcano is within 300 km of a major international airport, score = 2; if none of these criteria are met, score = 0.

1

Regional aviation exposure

This score is based on the log10 of approximate daily passenger traffic in each region. At present, in the U.S., this score ranges from 4 to 5.15. The regional risk code is applied only to type 1 volcanoes and those type 0 volcanoes that have produced explosive eruptions.

1.70

Power infrastructure

Is there power infrastructure (e.g., power generation/transmission/distribution for electricity, oil, or gas) within flowage hazard zones, or in an area frequently downwind of the volcano and close enough to considered at some risk? If yes, score =1

0

Transportation infrastructure

Is there transportation infrastructure (e.g., port facilities, rail lines, major roads) within flowage hazard zones, or in an area frequently downwind of the volcano and close enough to considered at some risk? If yes, score = 1

1

Major development or sensitive areas

Are there major developments or sensitive areas threatened (e.g., National Park facilities, flood control projects, government facilities, developed tourist/recreation facilities, manufacturing or other significant economic activity)? If yes, score =1

1

Volcano is a significant part of a populated island

Holocene volcanic deposits cover >25% of land mass. If yes, score = 1

1

Total of Exposure Factors

10.0
Sum of all hazard factors x Sum of all exposure factors = Relative Threat Ranking
80.0

 

Based on the Relative Threat Ranking of 80,  Fogo is a high risk volcano (the rating system includes five threat groups from very low to very high).

The main reason that Fogo is a high risk volcano is because of the relatively large number of people (800) that live within the caldera and directly in the lava flow zone.  In the 1995 eruption the towns within the caldera had to be evacuated and the lava flows and ash fall ruined the farmland and therefore hurt the economy.ıı  Fogo also has a history of erupting a few times each century,²² which means that eventually (in the next 50 years or so) there probably will be an eruption (though it may not be as large as the 1995 eruption).

Because of this Fogo should be a level 4 monitored volcano which means the following:

. LEVEL 4: Well-monitored Monitoring provides the ability to track detailed changes in real-time and to develop, test, and apply models of ongoing and expected activity.

·         Seismic – 12-20 stations are in place within 20 km of vent; including several near-field sites. Network includes numerous three-component instruments and a mix of other instrument types, including several digital broadband stations, acoustic sensors, and accelerometers. Borehole instruments are used where practicable. (Examples: Long Valley, Kilauea)

·         Deformation - Geodetic surveys are routine, and sufficient continuous stations (GPS, tiltmeters, and/or dilatometers) are installed to track closely geodetic unrest in space and time and do detailed source modeling to help distinguish among alternative mechanisms. (Examples: Long Valley, Kilauea)

·         Gas – Airborne or campaign gas measurements done frequently. A continuous monitoring array of several stations and other types of gas measurements (including DOAS) is deployed as appropriate for the volcano to enable quick identification of key geochemical changes.

·         Hydrologic - Level-3 coverage is available along with real-time monitoring of hill-slope soil moisture, stream discharge, etc. as appropriate. AFM systems are installed, where warranted, and supported by models predicting lahar size and area of impact.

·         Remote sensing – Level 3 coverage is available along with other data from all pertinent satellite sensors (e.g., daily multi-channel, high-resolution thermal-infrared images and frequent, high resolution, multi-channel visible images). Where practical, continuous ground-based thermal imaging and Doppler radar coverage is available for ash detection and eruption-rate estimates.

Required level of monitoring: 4

Current level of monitoring: 3

Using the scheme set up by the USGS the above description of level four monitoring is necessary for Fogo.  The current monitoring scheme for Fogo involves only 8 seismic stations, one of which is located on a nearby island.ı  See Current Monitoring Activities for more details on how Fogo is currently being monitored.  There is limited information out there on how Fogo is being monitored today, because the last published article about monitoring Fogo came out in 2003, and there is no real-time monitoring website produced by Cape Verde.

 

Citations within chart:

Population information from:

Faria, et al. "Monitoring Fogo Island, Cape Verde Archipelago, for Volcanic
     Hazard Mitigation." American Geophysical Union (Dec. 2001). Abstract.
     SAO/NASA ADS Physics Abstract Service. 24 Apr. 2008
     <http://adsabs.harvard.edu/abs/2001AGUFM.V21E..05F>.

Some idea of aviation info from: expedia.com

Transportation, sensitive areas, and infrastructure ratings based on info from:

Goike, Mike. "Climate and Geography." Sao Filipe de Fogo. 24 Apr. 2008
     <http://www.sao-filipe.com/html/geography.html>.

 

 

 
Questions about this site? Contact me @ cdavidow@mail.colgate.edu