Yasur Volcano

Yasur Volcano (361m) is located on Tanna, which is one of the southernmost islands of the Pacific state of Vanuatu. The volcano has been persistently active for hundreds of years and was seen erupting by Captain Cook in 1774. Eruptions have been largely strombolian and sometimes vulcanian since proper documentation began. Small lava lakes may also sometimes be visible in vents. Due to the type of activity and popularity as a tourist attraction, the volcano can be considered as the southern hemisphere equivalent of Stromboli volcano. Analysis of ashfall deposits suggests that 2 subplinian events may have occurred between 800 and 1400 years ago.

Yasur is a small largely basaltic pyroclastic cone located in the Yenkahe caldera (362m) which is one of several volcanic structures NE of the larger extinct Tukosmeru volcano (1084m). Yenkahe is itself located within the 4 km wide Siwi caldera which formed following eruption of the large andesitic Siwi pyroclastic deposits. Volcanism in the area is caused by the subduction of the Indo-Australian plate under the Pacific plate.

In June 2010, activity was at level 3 and involved several vents in both the north and south craters. These adjacent craters are seperated by a small ridge and together have a maximum diammeter of about 400 meters.

Classic strombolian eruption of Yasur Volcano	Yasur summit craters viewed from north rim

Map of Yasur volcano and surroundings located at car park

South Crater Activity

The southern crater is the main focus of tourist interest and a main viewing area exists about 150 meters from the inner rim of the crater. During early June, 2010, activity was of fluctuating intensity ranging from minor strombolian eruptions to powerful eruptions (at times in short succession) accompanied by visible shock-waves. At other times, eruptions of dense ash clouds were observed. No particular trend could be determined. Four distinct vents were involved in the activity of the southern crater.

Degassing was often intense. Yasur is known to be a major contributor to volcanic global sulphur dioxide emissions, with 7.9kg/sec being measured during a 2004-2005 study (Bani 2007. Geophys. Res. Lett. 34(20), p.6-9 ). This amounted to about 2% of global volcanic emissions of this gas.

Gas emissions have also been studies over short time periods, allowing analysis of gases associated with strombolian events in comparison to that emitted by steady degassing of the same vents (Oppenheimer et al. 2006. Appl. Phys. B 85, p.453-460). Using Fourier Transform Infrared Spectroscopy (FTIR), it was shown that the ratio of sulphur dioxide to hydrogen chloride emitted was about 2:1 during passive emission phases, but peaked at around 30:1 in gas pulses released by explosions. This is explained by the fact that the gas pockets rising in the conduit that cause strombolian eruptions are largely derived at depths where chlorine exsolution from the melt is minimal, whilst continuous degassing is from surface-proximal magma which both exsolves more chlorine and less sulphur due to prior depletion of the latter. Carbon dioxide and carbon monoxide levels showed no significant trends.

Significant degassing of S crater, ash eruption of N crater	Strombolian eruption	Strombolian eruption with minor ash output

View into south crater from west rim	Simultaneous activity at 3 vents	Four active vents in south crater

Closer view of vents 2-4	Ash eruption from vent "4", viewed from north rim

Ash eruption from vent "2" in south crater, viewed from north rim	Ash eruption of S crater viewed across degassing N crater

The seismicity associated with strombolian activity at Yasur volcano is unremarkable since similar to that at Stromboli volcano . Changes in seismic activity relating to such eruptions have been observed in response to a nearby M=7.3 earthquake (Battaglia et al. 2009. AGU Fall Meeting, Abs. S21A-1702). For more information on the mechanism underlying strombolian eruptions, the reader is referred to the section on Stromboli which deals with this issue in more detail. For detailed videos of strombolian activity see also section on Fogo Volcano.

Volcanic bomb on east rim of Yasur Volcano	Powerful ash-rich Strombolian eruption	Volcanic bomb on east rim of Yasur Volcano

Powerful ash-rich Strombolian eruption - bombs thrown hundreds of meters over crater	Volcanic bomb emplaced on E rim (5 m from my position) by eruption shown on left

South crater powerful Strombolian activity	South crater Strombolian activity

South crater Strombolian activity	South crater Strombolian activity

North Crater Activity

In early June, 2010, activity of the north crater was focussed at a complex of at least 2 closely spaced vents at the base of the crater, with a tiny nearby vent and fissure occasionally also involved in minor ash eruptions. Eruptions from the main vent regularly produced dense ash clouds heavily laden with volcanic bombs. Due to friction within these ash clouds frequent static discharges could be heard and often seen, especially at night. The activity threw numerous volcanic bombs onto the crater rim on several occasions, hence making the area extremely hazardous and an absolutely no-go area at night.

Ash clouds from northern crater	Ash clouds from northern crater

Minor ash eruption - summit of Yasur is high point at top right	Approaching the north crater

Ash clouds over northern crater	Ash clouds over northern crater

Ash clouds over northern crater	Ash clouds over northern crater	Ash clouds over northern crater

Ash clouds rising from northern crater	Ash clouds rising from northern crater	Ash clouds rising from northern crater

Onset of N crater powerful ash eruption	Partially laterally directed ash cloud	Onset of N crater powerful ash eruption

Three images from same eruption of the North crater viewed from SE in evening. Multple static discharges (lightning) occurred several seconds after onset of the eruption, once friction between particles in the building ash cloud had resulted in sufficient charge buildup.

Author with recently impacted large volcanic bomb on north rim	Recent "Dark" (non-juvenile) volcanic bomb impact crater east of north crater

Details of North Crater Vents including Animations:

Anmations showing 2 different eruptions from the North crater taken from a similar position on the rim to the ESE of the vents. It is evident that two distinct vents are involved as the eruptions start from different positions in the crater. The vents are obscured by fallback from previous eruptions (i.e. ash and other eruptates).

Vent on floor of N crater briefly visible on first observation day, adjacent vent ashing	Tiny vent W of crater bottom vent(s) - seemed to lie on small fissure

Surroundings of Craters / Ash Plain

The surroundings of Yasur are unusual in that an extensive largely unvegetated ash plain is found to its northeast, whilst the other flanks of the volcano are vegetated with dense forest until the immediate vicinity of the craters. The location of the ash plain corresponds to the area most commonly downwind of the volcano (i.e. the NW). Until 08.05.2000, the ash plain frequently housed a shallow lake (lake Siwi), however on this date the lake rapidly drained, causing damage to the downstream settlement at sulphur bay. To the east of Yasur and on its southern flank are the remnants of earlier volcanic structures.

River valley deeply eroded into ash plain	Footprint on ash plain

Yasur volcano viewed from ash plain	Yasur volcano viewed from ash plain	View from west, note vegetated south flank

Deposit of reddish rocks east of summit craters	Ash on leaves (Inset shows exceptionally high crystallinity)

View SE from south crater	Looking south from NE rim - Note red rock formations

Red rock plateau E of craters (location of car park)	Yasur crater complex viewed from east

Impact of Activity

The impact of Yasur is generally only local, although on June 1, 2010, flights in New Caledonia (over 400km SW) were slightly disrupted by ash from the volcano. However, this is unusual given that ash is rarely emitted to significant heights and usually simply dissipates over the Pacific ocean.

Ashfall usually merely represents a nuisance for the local population. Associated elevated flourine levels in local water are sometimes detectable but not highly significant and the relatively coarse ash was not associated with significant long-term health problems (Cronin and Sharp, 2002. Int. J. Env. Health Res. 12(2), p.109-123). Vegetation may be affected by volcanic gases in downwind areas, as is particularly evident from the location of the ash plain. Acidic rainfall and mist appears to be particularly problematic.

Periodic partial collapses of the cone only have local impacts due to its small size. In 1975, about 50000 cubic meters detached from the outer flank, ending at its base and leaving a 100m wide scar.

Visitor Information

Tanna Island is connected by daily flights from the capital of Vanuatu, Port Vila. The volcano is an about 2 hour drive from the airport. Several lodges are found near its base, including the "Jungle Oasis". The crater can be reached on foot in about 45 min from this lodge, although most tourists choose to be driven up to the car park right next to the summit region.

Whilst Yasur is one of the most accessible volcanoes in the world, the risk posed by the impact of volcanic bombs must not be underestimated, especially during periods of increased activity. Vanuatu's Natural Disaster Management Office regularly releases bulletins when activity levels are increased and had indeed released a bulletin (No.4, 27.05.2010) raising the alert level to 3 (on a scale of 0-4) shortly before the period (29.05.2010 - 06.06.2010) during which the images on this page were taken.

Dirt road leading up to the summit region	Post box at foot of walkway from car park to main viewpoint

Tourists watching eruptions at Yasur volcano	Tourists watching eruptions after nightfall

During periods of heightened activity, the summit region may be officially closed to visitors, yet tourists were still being guided to the crater rim when I visited, even though the activity was at level 3 and access was formally restricted. One night, numerous large volcanic bombs actually fell on the main viewpoint only hours after visitors had left. Whilst incandescent bombs can be seen glowing at night and can thus be avoided if seen, numerous non-juvenile ("black") bombs are also ejected by the volcano. These are invisible at night since they are not incandescent and thus represent a potentially fatal hazard. Indeed, several tourists have been killed or badly injured by the impact of volcanic bombs at Yasur volcano. For example, in 1994 and 1995 there were 3 fatalities, with one incident involving 2 people being killed by a 15 kg volcanic bomb. The velocity of volcanic bombs can reach as high as 250m/sec (Marchetti et al. 2008. AGU Fall meeting Abs. V51E-2083) and bombs can fall in the forest beyond the car-park during level 4 activity as seen in e.g. 1999. Fortunately activity tends to fluctuate gradually so that phases of extremely high activity can often be recognized.

The local guides should generally be able to provide up to date information and their advice should not be ignored by visitors.

Juvenile bomb (marked by helmet) lying on pathside rocks. Non-juvenile bomb crater is located just above helmet in image. Both found on tourist path in the morning after high activity.	Juvenile bomb recently impacting visitor viewpoint area.

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