Eruption 1986

[Nerio Cintron]

Therewere 75 confirmed eruptions at some point during 1986 from 67 different volcanoes; 41 of those were new eruptions that started during the year. A stop date with "(continuing)" indicates that the eruption was considered to be ongoing as of the date indicated. Data is reported through the last data update (6 June 2024). Information about more recent eruptions can be found in the Smithsonian / USGS Weekly Volcanic Activity Report.

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In 505 Swedish schoolchildren, the need to supervise the eruption of the maxillary canines was assessed by digital palpation and related to occlusal development and somatic maturity. The aim was to judge the extent to which clinical methods should be supplemented with radiographic methods. The 505 children, aged 8-12 yr, were clinically investigated and the eruption was followed over a 3-yr period. The age of the child was found not to be a valid criterion for radiographic investigation of the canine position. The investigation showed that 29% of 10-yr-old children had non-palpable canines bilaterally. In 11-yr-old children, the corresponding figure was 5%. A palpable buccal bulge in the primary canine apical area was found to signify a favorable eruption position. The prevalence of non-palpable or unerupted canines was 3% in the age group 11-15 yr. Indications for radiographic examination of canine position were present in altogether 7% of the children over 10 yr of age according to the clinical diagnostic criteria used.

A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in the waters and therefore the risk of further eruptions. Along with the Lake Monoun disaster two years earlier, it is one of only two recorded limnic eruptions in history.[6]

What triggered the catastrophic outgassing is not known.[7][8][9] Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake.[10][11] A third possibility is that cool rainwater falling on one side of the lake triggered the overturn. Others still[who?] believe there was a small earthquake, but because witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely.[citation needed] The event resulted in the supersaturated deep water rapidly mixing with the upper layers of the lake, where the reduced pressure allowed the stored CO2 to effervesce out of solution.[12]

It is believed that about 1.2 cubic kilometres (4.21010 cu ft) of gas was released.[13] The normally blue waters of the lake turned a deep red after the outgassing, due to iron-rich water from the deep rising to the surface and being oxidised by the air. The level of the lake dropped by about a metre[14] and trees near the lake were knocked down.[15]

Scientists concluded from evidence that a 100 m (330 ft) column of water and foam formed at the surface of the lake, spawning a wave of at least 25 metres (82 ft) that swept the shore on one side.[16]

It is a possibility that other volcanic gases were released along with the CO2, as some survivors reported a smell of gunpowder or rotten eggs, which indicates that sulfur dioxide and hydrogen sulfide were present at concentrations above their odour thresholds. However, CO2 was the only gas detected in samples of lake water, suggesting that this was the predominant gas released and as such the main cause of the incident.[17]

Reporters in the area described the scene as "looking like the aftermath of a neutron bomb."[18] One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:[4][19].mw-parser-output .templatequoteoverflow:hidden;margin:1em 0;padding:0 32px.mw-parser-output .templatequote .templatequoteciteline-height:1.5em;text-align:left;padding-left:1.6em;margin-top:0

I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible ... I heard my daughter snoring in a terrible way, very abnormal ... When crossing to my daughter's bed ... I collapsed and fell. I was there till nine o'clock in the morning (of Friday, the next day) ... until a friend of mine came and knocked at my door ... I was surprised to see that my trousers were red, had some stains like honey. I saw some ... starchy mess on my body. My arms had some wounds ... I didn't really know how I got these wounds ... I opened the door ... I wanted to speak, my breath would not come out ... My daughter was already dead ... I went into my daughter's bed, thinking that she was still sleeping. I slept till it was 4.30 in the afternoon ... on Friday (the same day). (Then) I managed to go over to my neighbours' houses. They were all dead ... I decided to leave ... (because) most of my family was in Wum ... I got my motorcycle ... A friend whose father had died left with me (for) Wum ... As I rode ... through Nyos I didn't see any sign of any living thing ... (When I got to Wum), I was unable to walk, even to talk ... my body was completely weak.

Following the eruption, many survivors were treated at the main hospital in Yaound, the country's capital. It was believed that many of the victims had been poisoned by sulphur-based gases. Poisoning by these gases would lead to burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled.[9]

Interviews with survivors and pathologic studies indicated that victims rapidly lost consciousness and that death was caused by CO2 asphyxiation.[20] At nonlethal levels, CO2 can produce sensory hallucinations, such that many people exposed to CO2 report the odor of sulfuric compounds when none are present.[20] Skin lesions found on survivors represent pressure sores, and in a few cases exposure to a heat source, but there is no evidence of chemical burns or of flash burns from exposure to hot gases.[20]

The scale of the disaster led to much study on how a recurrence could be prevented.[21] Several researchers proposed the installation of degassing columns from rafts in the middle of the lake.[22][23] The principle is to slowly vent the CO2 by lifting heavily saturated water from the bottom of the lake through a pipe, initially by using a pump, but only until the release of gas inside the pipe naturally lifts the column of effervescing water, making the process self-sustaining.[24]

Starting from 1995, feasibility studies were successfully conducted, and the first permanent degassing tube was installed at Lake Nyos in 2001. Two additional pipes were installed in 2011.[24][25] In 2019 it was determined that the degassing had reached an essentially steady state and that a single one of the installed pipes would be able to self-sustain the degassing process into the future, indefinitely maintaining the CO2 at a safe level, without any need for external power.[26]

Following the Lake Nyos disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. In 2005, Lake Kivu in the Democratic Republic of the Congo, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence that outgassing events around the lake happened about every thousand years.[27]

However, a study undertaken in 2018 and released in 2020 found flaws in the 2005 study, including a possible bias in the conversion of concentrations to partial pressures, to an overestimation of concentrations, or to a problem of calibration of sensors at high pressure. The 2020 study found that when these errors were accounted for, the risk of a gas eruption at Lake Kivu did not seem to be increasing over time.[28]

The first sign of activity atMount St. Helens in the spring of 1980 was a series of small earthquakes thatbegan on March 16. After hundreds of additional earthquakes, steam explosions onMarch 27 blasted a crater through the volcano's summit ice cap. Within a weekthe crater had grown to about 1,300 feet in diameter and two giant crack systemscrossed the entire summit area. By May 17, more than 10,000 earthquakes hadshaken the volcano and the north flank had grown outward at least 450 feet toform a noticeable bulge. Such dramatic deformation of the volcano was strongevidence that molten rock (magma) had risen high into the volcano

Within 15 to 20 seconds of a magnitude 5.1 earthquake at8:32 a.m., the volcano's bulge and summit slid away in a huge landslide - thelargest on Earth in recorded history. The landslide depressurized the volcano's magma system, triggering powerful explosions that ripped through the slidingdebris. Rocks, ash, volcanic gas, and steam were blasted upward and outward tothe north. This lateral blast of hot material accelerated to at least 300 milesper hour, then slowed as the rocks and ash fell to the ground and spread awayfrom the volcano; several people escaping the blast on its western edge wereable to keep ahead of the advancing cloud by driving 65 to 100 miles an hour!The blast cloud traveled as far as 17 miles northward from the volcano and thelandslide traveled about 14 miles west down the North Fork Toutle River.

The lateral blast produced a column of ash and gas(eruption column) that rose more than 15 miles into the atmosphere in only 15minutes. Less than an hour later, a second eruption column formed as magmaerupted explosively from the new crater. Then, beginning just after noon, swiftavalanches of hot ash, pumice, and gas (pyroclastic flows) poured out of thecrater at 50 to 80 miles per hour and spread as far as 5 miles to the north.Based on the eruption rate of these pyroclastic flows, scientists estimate thatthe eruption reached its peak between 3:00 and 5:00 p.m. Over the course of theday, prevailing winds blew 520 million tons of ash eastward across the UnitedStates and caused complete darkness in Spokane, Washington, 250 miles from thevolcano.

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