Hazards

Hazard Map Assessment for Volcan Villarrica and the surrounding area:

Reserved: Volcan Villarrica has produced a wide array of eruption styles, from Hawaiian to Plinian, making it very hard to create a comprehensive, and yet practical, hazard map. For this reason I decided to narrow down my hazard map and focus on the threat of lahars, which is the biggest threat the populations around the volcano face. Villarrica, as a stratovolcano in a high-latitude region, has massive glaciers that cover the summit and flanks of the volcano. Because of this, if the volcano sees almost any increase in magmatic activity that would cause it to heat up, even if it doesn’t erupt, this added heat could trigger a lot of melting of the mountains glaciers, thus producing lahars.⁹

The only known cause of death Villarrica has incurred is due to lahars, which I believe reinforces the fact that lahars are the most serious danger the volcano poses. While it has been proven that Villarrica has produced large Plinian eruptions in the past, with pyroclastic flows and surges, as well as large amounts of tephra fallout, the likelihood of a similar style eruption occurring, I believe, is very low. Also, if such an eruption occurred, evidence suggests that the pyroclastic flows would barely, if at all, make it down the flanks of the volcano, thus threatening no one, as no one lives on the flanks of the volcano. Also the predominant wind direction of the region would blow tephra fallout to the South Southeast, which, being largely national park land, is very sparsely populated. ⁹

I have superimposed a zone (brown area) on top of a satellite image of Villarrica that represents the areas future lahars could affect. This zone is based on the evidence of routes past lahars have taken, as well as the major drainage basins of the volcano. As is shown in the North-central area of the map, the tourist town Pucon, the largest population center near the volcano, lies right in the lahar hazard zone.⁹

Villarrica Hazard Map

***THIS HAZARD MAP IS NOT OFFICIAL!!***

Map Source: ¹¹

Other Risks: Economic, etc.

There are a number of risks to the population surrounding Villarrica if it does erupt soon, some of which have already been discussed. One risk that may not seem obvious is the risk to the local economy. As the economy around the volcano, especially the national park area and Pucon, relies heavily on tourism, an eruption, or even a false alarm called on the volcano, could wreak havoc on the economy. Not only would Pucon be in great risk of impending lahars, it would also be at risk of losing much of its revenue if tourists get scared away or are barred from entering the city.

Hazard Threat Assessment for Volcan Villarrica based on:

National Volcano Early Warning System

From PDF by John Ewert, USGS Open-File Report 2005-1164. ⁶

Hazard and exposure factors used in threat assessment of U.S. volcanoes for the National Volcano Early Warning System. See appendix text for discussion and explanation of abbreviations.
Hazards Factors		Score
Volcano type		1
Maximum Volcano Explosivity Index (VEI)		2
Explosive activity		1
Major explosive activity		1
Eruption recurrence		4
Holocene pyroclastic flows?		1
Holocene lava flows?		1
Holocene lahars?		1
Holocene tsunami(s)?		0
Hydrothermal explosion potential?		1
Sector collapse potential?		0
Primary lahar source?		1

Historical Unrest Factors	Score
Observed seismic unrest Since the last eruption, in the absence of eruptive activity, within 20 km of the volcanic edifice?	1
Observed ground deformation Since the last eruption, in the absence of eruptive activity, inflation or other evidence of magma injection?	0
Observed fumarolic or magmatic degassing Since the last eruption, in the absence of eruptive activity, either heat source or magmatic gases?	1
*Total of Hazard Factors*
Exposure Factors
Log₁₀of Volcano Population Index (VPI) at 30 km	4.7
Log₁₀of approximate population downstream or downslope	4.4
Historical fatalities?	1
Historical evacuations?	1
Local aviation exposure	1
Regional aviation exposure	3.25
Power infrastructure	0
Transportation infrastructure	0
Major development or sensitive areas	1
Volcano is a significant part of a populated island	0
*Total of Exposure Factors*	*16.35*
*Sum of all hazard factors x Sum of all exposure factors = Relative Threat Ranking*	*261.6*

With a score of 261.6, Volcan Villarrica is considered a HIGH RISK volcano. While this rated is probably fairly accurate, it may be a little skewed for the following reasons:

1). In the rating system, Villarrica received the highest score (4) for frequency of eruptions. Villarrica also has a history for producing large, explosive eruptions. Usually these two characteristics do not coincide in a volcano's eruptive history; a volcano is usually exploxive, and erupts infrequently, or it is non-explosive and erupts frequently. To account for this anomaly, Villarrica's potential to produce a wide range of lavas should be considered. As mentioned in the tectonic setting, Villarrica can produce both basaltic and andesitic lava, and therefore is capable of producing fairly effusive eruptions as well as large eruptions. So, Villarrica, while it does erupt often, rarely produces a large, explosive eruption.

2). Situated in a national park, the permanent population in close proximity to the volcano is pretty small. But, as the area has a large tourism industry in all seasons, the local population is greatly increased throughout the year, especially in the summer months. I decided to use population statistics that include the tourist population, as it is more realistic to assume that there will probably be the average amount of tourists present when an eruption takes place.

Given the hazard assessment data I have collected, I have a few suggestions for mitigating risks. First, I think an acoustic monitoring system for lahars would greater improve the safety of the area. This monitoring system would allow local residents more time to reach safety if a lahar was coming their way. Second, if a large eruption does occur, I would recommend evacuating the surrounding area (the national park, Pucon, Villarrica, countryside within 10 km).

The following is the template that helped me come up with my hazard assessment score:

Table 2. List of the 15 hazard and 10 exposure factors used in the NVEWS threat assessment and their scoring ranges. Detailed explanation of the factors is given in Appendix 2.
Hazard Factors	Scoring Ranges
Volcano type	0 or 1
Maximum Volcanic Explosivity Index	0 to 3
Explosive activity in past 500 years?	0 or 1
Major explosive activity in past 5000 years?	0 or 1
Eruption recurrence	0 to 4
Holocene pyroclastic flows?	0 or 1
Holocene lahars?	0 or 1
Holocene lava flow?	0 or 1
Hydrothermal explosion potential?	0 or 1
Holocene tsunami?	0 or 1
Sector collapse potential?	0 or 1
Primary lahar source?	0 or 1
Observed seismic activity	0 or 1
Observed ground deformation	0 or 1
Observed fumarolic or magmatic degassing	0 or 1
*Total of Hazard Factors*
Exposure Factors
Log₁₀of Volcano Population Index (VPI) at 30 km	0 to 5.4
Log₁₀of approximate population downstream or downslope	0 to 5.1
Historical fatalities?	0 or 1
Historical evacuations?	0 or 1
Local aviation exposure	0 to 2
Regional aviation exposure	0 to 5.15
Power infrastructure	0 or 1
Transportation infrastructure	0 or 1
Major development or sensitive areas	0 or 1
Volcano is a significant part of a populated island	0 or 1
*Total of Exposure Factors*
*Sum of all hazard factors X Sum of all exposure factors = Relative Threat Ranking*

Hazard and exposure factors used in threat assessment of U.S. volcanoes for the National Volcano Early Warning System. See appendix text for discussion and explanation of abbreviations.
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
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
Explosive activity If explosive activity (VEI ≥ 3) within the last 500 years: Score = 1
Major explosive activity If major explosive activity (VEI ≥ 4) within last 5000 years: Score = 1
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
Holocene pyroclastic flows? If yes: Score = 1
Holocene lava flows? If Holocene lava flows have traveled beyond the immediate eruption site or flanks and reached populated areas: Score =1
Holocene lahars? If Holocene lahars have traveled beyond the flanks and reached populated areas: Score =1
Holocene tsunami(s)? Has it produced a tsunami within the Holocene? If yes: Score = 1
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
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
Primary lahar source? If volcano has a source of permanent water/ice on edifice, water volume > 10⁶m³: Score = 1

Cont’d.

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
Observed ground deformation Since the last eruption, in the absence of eruptive activity, inflation or other evidence of magma injection? If yes: Score = 1
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
*Total of Hazard Factors*
Exposure Factors
Log₁₀of 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.
Log₁₀of 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).
Historical fatalities? If yes, and a permanent population is still present: Score = 1
Historical evacuations? If yes, and a permanent population is still present: Score = 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.
Regional aviation exposure This score is based on the log₁₀of 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.
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
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
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
Volcano is a significant part of a populated island Holocene volcanic deposits cover >25% of land mass. If yes, score = 1
*Total of Exposure Factors*
*Sum of all hazard factors x Sum of all exposure factors = Relative Threat Ranking*

Source: ⁶

Reserved:

Historical Unrest Factors

Score

Observed seismic unrest

1

Observed ground deformation

0

Observed fumarolic or magmatic degassing

1

Total of Hazard Factors

Exposure Factors

Local aviation exposure

1

Regional aviation exposure

3.25

Power infrastructure

0

Transportation infrastructure

0

Major development or sensitive areas

1

Volcano is a significant part of a populated island

0

Total of Exposure Factors

16.35

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

261.6