Vanuatu Volcano Alert Bulletin n°8 - Ambrym Activity (10 October 2019)

Report
from Government of Vanuatu
Published on 10 Oct 2019 View Original
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AMBRYM VOLCANO
16°15’00”S 168°07’00”E Summit Elevation 4377ft (1334m)
Current Vanuatu Volcano Alert Level: Level 1

Ambrym volcano is now in the minor unrest state. The Volcanic Alert Level is lowered from Level 2 to Level 1.

The current volcanic activity at Ambrym is consistent with Volcanic Alert Level 1. New scientific analysis suggest three (3) possible scenarios as the future volcanic activity for Ambrym in the short-term. These are:

1) Most likely; activity continues at current unrest level. This scenario (1) means that the Ambrym volcano activity consist mainly of obvious steam from the eruptive vents inside the summit craters (Benbow and Marum including Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu) like it was in 2001-2017. We consider this scenario 1 is likely as the volcano has just had a fissure eruption in December 2018 that induced the drainage of the lava lakes at the summit caldera and the Eastern Rift Zone down to the coast. Volcanic hazards remain about the summit craters area and the South East part of Ambrym Island (e.g. major cracks from 2018).

2) Not very likely; activity to decline to a lower level. This scenario (2) means that the Ambrym volcano activity will become even less than now. We consider this scenario 2 is less likely as Ambrym is a very active volcano and will in the short-term always have some form of volcanic unrest or activity. Activity would remain at the summit craters with minor volcanic hazards (risk).

3) Not very likely; unrest activity to increase and eruptive activity to restart. This scenario (3) means that the Ambrym volcano could undergo another eruptive phase at the summit area. We consider this scenario 3 is unlikely as the volcano has just finished a moderate eruption episode and has not recovered. This activity, if it does occur, would consist of explosive activity with volcanic ashes and gases emission from the eruptive vents inside the summit craters (Benbow and Marum). The activity may impact communities on Ambrym. Hazards and activity could be like it was from 2018.

Although volcanic activity has declined to unrest level, some volcanic hazards do remain on Ambrym specifically at the summit and eastern part of the Island. These are related to the presence of cracked areas. In addition to the summit hazards, the presence of active rifts and faults (major ground cracking) at the South-East area of Ambrym are also hazardous, they will continue to be eroded and affected by earthquake activity. The danger zones at the summit caldera remains at 1 km around Benbow and 2 km around Marum craters including Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu (See Safety Map Fig.1). The danger zone for life safety remains limited at the Permanent Exclusion Zone at Benbow and Danger Zone A at Marum. An additional danger zone at the South-East of Ambrym is now within 500 meters from major cracks.

Open cracks in the South-East Ambrym that formed during the December 2018 eruption may continue to open due to erosion. Major earthquake activity could continue to affect these cracks and weak layers or areas around the actives craters.

Latest field observations confirm that the Ambrym volcano activity has declined and conditions become stable. There is no significant manifestation of its volcanic activity and we now recognize the activity as minor unrest. The lava lakes that used to appear in Benbow and Marum craters have disappeared since the December 2018 eruption. The remaining activity inside both craters consist mainly of steam emissions. People from Ambrym and neighbouring islands will not see the volcanic glow at nights and the gas plume.

The Volcanic Alert Level for Ambrym has been at the Level 2 since 14th February 2019. Observations of the current activity are consistent with Volcanic Alert Level 1 activity. Level 1 indicates “Minor unrest. Danger zone remains at 1 km around Benbow, 2 km around Marum and 500 meters from major cracked areas in the South-East part of Ambrym”. Nevertheless, it is a useful reminder that eruptions can occur with little or no warnings.

Ambrym volcano is a very active volcano in Vanuatu with large caldera of 12 km in diameter and 2 active craters, Marum and Benbow. The volcano has been active during historical time at both summit and flank vents, producing moderate explosive eruptions and lava flows that have reached the coast. The larger events include eruptions in 1820, 1894, 1913 or 1929. Over the last seventy years (before the 2018 eruption), there have been no eruptions that extended beyond the summit caldera. The eruption of 1988 and 2015 are focused in the caldera. The December 2018 eruption was focused in the summit caldera, and also affected the Eastern Fracture or Rift Zone with ground deformation, rifting, faulting and uplift, but no eruption occurred there.

All tourism agencies, local authorities, people of Ambrym and the general public are advice that due to the presence of cracked areas at the caldera, the danger zone remains at the Permanent Exclusion Zone at Benbow and the Danger Zone A at Marum which are set about 1 km radius from Benbow and 2 km radius from Marum. There are life safety hazards within these hazard zones. Due to the presence of active rifts and faults at the South-East area of Ambrym, communities concerned are advised not to access within 500 meters from major cracks (Danger Zone). There is a possibility (low) that earthquake or volcanic activity may start from this area. More information about the hazards can be found here on the Ambrym Volcano Advice Key Messages: https://www.vmgd.gov.vu/vmgd/index.php/geohazards/volcano/volcano-info/r....

The Vanuatu Meteorology and Geohazards Department continues to closely monitor this volcano activity. More information will be provided as soon as necessary.

For further information, please contact Geohazards Division at the Vanuatu Meteorology and Geohazards Department at geohazards@meteo.gov.vu or 24686.