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Volcanic Advisory 4

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Summary
15 January 2015 Observations confirm an ongoing eruption from a new island between Hunga Tonga and Hunga Ha’apai, 65 km from Nuku'alofa.

We have reviewed observations collected during a visit to the erupting volcano in the Hunga Tonga-Hunga Ha’apai region on January 14. A new island has been built by the eruption between the existing islands of Hunga Tonga and Hunga Ha’apai, and is now joined to Hunga Ha’apai.

The new island is more than 1 km wide, ~2km long and about 100 m high. During our observations the volcano was erupting about every 5 minutes. Dense ash was being erupted to a height of about 400 m, accompanied by some large rocks. Higher we observed mostly steam, but with some ash. Above about 1000 m, the eruption plume was almost exclusively steam. As the ash is very wet, most is being deposited close to the vent, building up the new island.

Hazardous surges of ash and steam were seen to spread out horizontally during eruptions, and these extended more than 1 km from the erupting vent.

Ash fall and acidic rain was observed within 10 km of the eruption. Leaves on trees on Hunga Tonga and Hunga Ha’apai have died, probably caused by volcanic ash and gases.

No large rafts of pumice or other floating volcanic debris were observed. Strong smells of volcanic gases were noticed on a few occasions.
This eruption is similar to that at Hunga Ha’apai in 2009, but only producing larger volume of materials resulting in the size of the island.
It is unclear at this stage if there is any relationship between the eruption and a red algal bloom observed in seawaters around Tonga recently.

Introduction
This is the fourth advisory of the volcanic activity over Tonga. The advisories had been based on collective information provided by Tonga Broadcasting Commission, Tonga Meteorological Services, Tonga Airport Limited, NZ-Meteorological Services, His Majesty’s Armed Force, National Emergency Management Office, and Ministry of Lands and Natural Resources. The content of this edition is largely contributed to by information from a site observation conducted on the 14th January 2015 sponsored by the New Zealand High Commission.

Eruption Location
The eruption is located between Hunga Tonga and Hunga Ha’apai (Figure 1). This was confirmed during the site visit. The eruption was first reported on 20th December 2014 by fishermen to be on the eastern side of Hunga Ha’apai with no visuals. This was assumed to be the vents in the southern side as indicated in the previous advisory. Daily reports from pilots did not provide definite location of the eruption due to cloud cover. On 6 January 2015 the Tonga Navy provided images of the eruptive activity which appeared to from Hunga Ha’apai given the angle of the camera and visibility through the rain. The images indicated nothing from the area of the submarine vents. The first official site visit on 14 January confirmed the location of the eruption at last.

The eruption area located approximately 65km NW of Vuna Wharf, Nuku’alofa, and ~70km SW of Nomuka Island.

Figure 1. Location map showing the new island formed between Hunga Ha'apai and Hunga Tonga, 65 km north-west of Nuku'alofa. The island (marked yellow) is over 1 km in diameter. The crater (marked red) is estimated 400-500m.

Figure 2. A view from the SE positioning the vent in between Hunga Ha’apai (left) and Hunga Tonga (right). Note the rise of the ash clouds above the crater after the line of clouds at ~250m elevation. The dark clouds within 5km of the eruption gives acid rain with ash.

Figure 3. Westward view of the crater being cleared of ash and gas. The summit of the crater ~90m elevation with a crater width of 400-500m.

Figure 4. Eruption of ash and tephra (in black and dark grey).

Figure 5. View from the SW of gas shooting through the initial eruption of ash at ~300m.

Figure 6. North westward view of the eruption. Note the horizontal spread of the ash like material left and right at above 1,000m.

Figure 7. South westward of the eruption. Note Hunga Tonga on the right, and southern edge of Hunga Ha’apai over the southern slope of the new island.

Figure 8. South eastward of the eruption. Hunga Tonga on the left, and Hunga Ha’apai on the left. The steam rising over 1000m altitude.

Figure 9. Northward view of the eruption. Hunga Tonga in the background. The summit of the crater in the left towards Hunga Ha’apai, and note the dark clouds above at ~200-300m

Volcanic Ash Forecasting
Pilots have reported steam plumes from the Hunga Ha'apai and Hunga Tonga area, but substantial ash emission to the altitudes at which aircraft fly have not been observed for several days.

Airline Flights
International flights resumed on the 14 January after several days of cancelled flights. The domestic airline is currently also operating.

Conclusion
The eruption of ash and tephra continues, but in recent days the presence of ash has been limited to low elavations.
Observations on 14 January 2015 confirms the location of the eruption that there is only one source of the eruption, a new island between Hunga Tonga and Hunga-Ha’apai.

Contact & Further information
For further information contact the Natural Resources Division of the Ministry of Lands and Natural Resources at Telephone 25508 or Email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated ( Thursday, 22 January 2015 11:57 )  

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