1. Volcanic gases, “A telegram from the Earth’s interior” -Sadao Matsuo
Direct health hazards
Radon, H2S, CO2
Dense gases collect in low areas
Indirect effects (SO2, H2SO4, HCl, HF)
Acid rain
Destruction of crops (Laki)

2. Large volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrochloric acid (HCl), hydrofluoric acid (HF) and ash (pulverized rock and pumice) into the stratosphere. CO2 is a greenhouse gas and contributes to global warming. HCl and HF can dissolve in water and fall to the earth as acid rain. Most of the SO2 is slowly converted to sulfuric acid (H2SO4), which condenses into a mist of fine particles. These sulfate aerosols reflect radiation from the Sun, cooling the troposphere; they also absorb the Earth's heat, warming the stratosphere. The aerosols also promote ozone destruction by altering chlorine and nitrogen chemical species in the stratosphere. As the aerosols settle down into the upper troposphere, they can serve as nuclei for cirrus clouds, further affecting the Earth's radiation balance.

3. 2006: Three Die From Toxic Gases At California Ski Resort: Volcanic Fumes Claim Ski Patrol Members (Mammoth Mountain)
Volcanic gases: a driving force, a symptom of unrest, AND a direct hazard through contact and climate change

4. Trees killed by elevated CO2 in soil near Horseshoe Lake, at foot of Mammoth Mountain

5. Mazuku (Swahili for "evil wind") hazard,
CO2 >15 wt%
Associated with rifting,
Near Goma, shore of Lake Kivu, DRC
“Elephant graveyards”

7. Lakes Nyos and Monoun, Cameroon
Volcanic CO2 builds up in lower reaches of lake
Lake overturn releases large amounts of gas
1984: Monoun (36 fatalities)
1986: Nyos (~1800 fatalities)
In both cases, without prior notice, a cloud of dense gas erupted from the lake, covering the surrounding area under a deadly blanket several tens of meters thick, for an unknown amount of time. The source of the gas became clear in the aftermath of the disasters, since the normally clear waters of the lakes turned reddish and the lake shores were severely disturbed by waves and strong winds. No one in the path of the cloud managed to escape its lethal effects. Skin discoloration found on some victims were tentatively interpreted as burns, but this diagnosis is still controversial. Witnesses on topographic hights report a loud noise originating from the lake and, in the case of lake Nyos, flashes of light visible over the lake ; both disasters occurred at night, darkness adding to the mystery of these dreadful natural catastrophes.  From:

8. Rapid degassing from lakes
Lake Nyos in Cameroon, 1986, 1800 people died from asphyxiation.
1 km3 of CO2 was released
When the lake overturns suddenly, depressurization of this water results in rapid exsolution of the gas and its liberation to the atmosphere. The high density of cold CO2 relative to ambient air allows the gas cloud to flow down topographic depressions and accumulate locally.

9. Cameroon Lakes: mediation
Group of French and Cameroonian scientists did the project with partial funding from US (lots of funding from Cameroonian govt)
- 1987: publication of the "Livre blanc" on the degassing project of lakes Nyos and Monoun by J. C. Sabroux, French Ministry of Environment, : first demonstration of the self-siphon process at Nyos and Monoun with one cm diameter pipes, : successful self-siphon at Monoun using 50 mm and 145 mm diameter pipes, : successful experiment at Nyos: a 20 metres fountain was triggered using a 145 mm diameter pipe, the first permanent degassing fountain at Nyos (50 m in height), : the first permanent fountain at Monoun (8 m in height).
The first permanent degassing column will be assembled and set up in January 2001 at Nyos. The main part of the funding comes from the US Office of Foreign Disaster Assistance (OFDA). The French Embassy in Yaounde and, of course, the Cameroonian Government also participate in the financial and logistical support.

10. H2S: hydrogen sulfide, “rotten eggs” Adatara, Honshu, Japan
1997: four hikers in summit caldera died from inhalation of H2S
September 15, 1997
Four hikers lost their lives when they fell into a summit crater on Adatara Volcano in Japan. They probably died due to inhalation of H2S in the bottom of the crater. Public warnings were given to stay away from the volcano, as activity has increased there over the past few years. This increased activity has included mud spouting from ponds on the crater floor and increased fumarolic activity. (from

11. Acid rain/haze Laki, Iceland HF kills livestock
Laki – HF was responsible for much of the livestock fatality
Masaya Volcano, Nicaragua

12. Effects of long-term exposure
CO2: no adverse effects in low concentrations
Radon (Rn)
Carcinogenic
SO2, H2SO4 (sulfuric acid), HCl (hydrochloric acid)
Dangerous for those with heart conditions
Erosion of teeth
Skin rash
Irritation of nose, throat, lungs
HF (hydrofluoric acid)
Changes in bone structure, chronic irritation of nose, throat, lungs

13. Vog and Laze
Vog (volcanic smog) is a mixture that includes gases but is predominately aerosols (tiny particles and droplets) formed when volcanic gas reacts with moisture, oxygen, and sunlight
Lava from Kilauea reaches the Pacific, where it vigorously reacts with cold seawater to create large steam plumes laden with hydrochloric acid. These plumes are called "laze."