Yasur Volcano – Yenkahe Caldera
Yasur, located at the SE tip of Tanna Island, is a mostly unvegetated 361-m-high scoria cone with a nearly circular, 400-m-wide summit crater.
Yasur is the most frequently visited of the Vanuatu volcanoes.
It has been in more-or-less continuous activity since Captain Cook observed ash eruptions in 1774.
This style of activity may have continued for the past 800 years.
Yasur is a basaltic scoria cone that typically has up to five active vents.
These produce a combination of two eruption types
- Strombolian - bubbles of glowing magma burst, spraying bombs of lava into the air
- Vulcanian – explosions that burst through a blocked vent, generating showers of bombs and also clouds of fine ash, which blow downwind
Erupted Magma is up to 1000°C and bombs remain very hot for up to an hour from eruption. Ash is not hot.
Yasur’s summit is 361 m above sea level and the crater is 600 m across at its widest point.
Yasur is the youngest of a group of Holocene volcanic centres constructed inside a larger volcanic caldera.
The Yenkahe caldera is a 4-km-wide, horseshoe-shaped depression that collapsed during two large eruptions that blanketed almost all of southern Tanna in thick ash and scoria. This deposit forms the cliffs along the SE and S coasts.
This huge block of ground beside Yasur has been pushed up, probably by magma underground.
Groundwater heated by the magma comes up fractures around the Yenkahe hill.
Earthquakes and ground movement
Earthquakes in this area have raised the Yenkahe hill and Port Resolution Harbour more than 20 m during the past 300 years.
Vanuatu volcanism is caused by subduction of the Indo-Australian plate below the Pacific plate under Vanuatu.
A large magma chamber is located a few km below Yenkahe caldera, feeding Yasur and pushing up Yenkahe hill and ajacent areas.
There are a seismograph, two cameras and a microbarometer stationed at Yasur, monitored remotely by VMGD in Port Vila.
The data and photos can be seen at: http://www.geohazards.gov.vu/
Bombs can land in any zone at any time.
The only way to avoid all risk of bombs is to stay off of Yasur.
Stay out of the permanent exclusion zone – the danger is extreme
The exclusion zone may be extended - during periods of larger or more frequent explosions to include Zone A, or to include Zone A & B.
Check which zone(s) are closed in the latest bulletin - click on ‘Tanna’ at:
Flying bombs are always a danger- Wear a hard hat, it will help protect you, but it will not stop larger bombs.
Watch for bombs in the air especially after explosions. Stand still unless you see bombs that are not moving left/right or up/down – these are coming towards you, and you should avoid them.
Bombs fly very fast – even though they look to move slowly at first. The time from an explosion to bombs landing at the rim is often only a few seconds.
Falling into the crater – beware that the edge of the crater is slippery and unstable.