S C H O O L O F E N V I R O N M E N T

Hunga Ha’apai-Hunga Tonga – birth of a new volcano and discovery of

a new caldera

Shane Cronin with help from: Marco Brenna, Ian Smith, Simon Barker, Manu Tost, Brendan Hall Murray Ford, Sisi Tonga’oneva, Taaniela Kula, Rene Viaomounga and Paul Taylor

Tongan Arc One of the fastest crustal collision settings on Earth

A chain of volcanic islands to the west Inhabited islands, uplifted coral platforms to the east

Tongan Volcanic Arc

Hunga Haapai

Red: Volcanoes Green: Inhabited Islands

Fonualei Kao Tofua

Tonga – Unusual silicic and explosive volcanoes

Tofua Ignimbrite Tofua: Two major eruptions led to caldera collapse ~1000 and ~800 years B.P. Likely generated tsunami as well as widespread ash

Tonga archaeological/vegetation history

Highly fertile soils – “andisols” volcanic ash based Three sudden major changes in vegetation composition on in last 3000 yrs B.P. Legends of major explosive eruptions

Archaeology shows sudden changes in agricultural practices and technology

Kotu Island

Tongatapu Island

Tonga – Big eruptions and thick ash layers

Volcanic ash deposits show that ash is blown >70 km to the East Soils and swamps contain the best records

Fotuha’a Island Foa Island Ha’afeva Island

Vava’u

Ha’afeva

Swamp

Swamp

Matuku Island – tephra/soil sequence

Tongatapu (pop. 71,000)

Estuary

Volcanic deposition sites

Chronology and database of ash records

Radiocarbon dating (28 new dates) reveals 12 major eruptions, and >20 smaller ones others from a range of sources over last 6700 years

Single-grain chemistry Correlate ash from cores on Ha’afeva and Foa to major eruptions of Tofua.

Hunga Ha’apai, Hunga Tonga (HH)

Pleiade, Satellite, Jul. 2014

Hunga – submarine volcano

Hunga (one of a chain!) Unusual flat top Active history Small eruptions in: 1912, 1937, 1959, 1988, 2009, 2015 What is the bigger picture? Is it a source of some of the major tephra horizons on Tongatapu?

1988 eruption

N

2009 eruption

Several days in June 1988, Fissure or chain of cones in shallow water at about 1 km SSE of Hunga Ha’apai

Month-long, surteseyan eruption in March 2009, tuff cone construction, rapidly eroded away, little geological study

2014-2015 Eruption Nov-Dec 2014 – earthquakes, eruption confirmed on 19 Dec 14 Surface eruptions at two sites, columns 3 km+ into Jan 2015 Plumes up to 9 km from Jan 11, flights diverted and cancelled Eruption ceased in late January

2014-2015 Eruption Surtseyan emergent hydrovolcanic eruptions – vigorous/highly energetic base surges, tephra jetting, fall and oblique fall of jets, saturated deposits, debris flows and syn-eruptive slumping 6 Jan 2015 – Tongan Navy

14 Jan 2015 – Base surges

15 Jan 2015 – NZ High Commission

14 Jan 2015 7 Jan 2015

21 Dec 2015

Rapid Island growth

140 m high and 2.5 km diameter island built over 3 weeks

Coastal and surface erosion of the island

January 2015 May 2016

Landing party study

Tombolos joined the islands: “easy” access to the geology of the older Islands

Hunga Tonga

Hunga Ha’apai

Surveying

Drone/RTK surveys

Studies into new deposits

Older volcano - Hunga Tonga

Stacked lava flows show the flanks of a large former volcano

Hunga Tonga – evidence for recent uplift

Hunga Ha’apai

Clues to violent past

Hunga Ha’apai – remnants of 2009 deposits

Hunga Ha’apai – 2009/2015 deposits

Hunga Ha’apai Pyroclastic

flow deposits!!

Hunga Ha’apai

Partly welded – high temperature, violently emplaced, pyroclastic flow deposits Evidence of past caldera-forming eruptions Charcoal is 965 ± 20 yrs B.P. – correlates to a volcanic ash layer on Tongatapu

5-10 cm lapilli 840 ± 60 yrs B.P.

5-10 cm lapilli 1530 ± 70 yrs B.P.

10-20 cm lapilli 900 ± 40 yrs B.P.

Tongatapu ash layers

Most life destroyed, but returning colonisers

Surge impacts

Crater modification and erosion

Recovery of ecosystem

Caldera

GT “Island”

1988 Cones

Dog-tooth Cones

Cones

Cones

WASSP Multibeam bathymetry Survey

Hunga Caldera 4 km diameter North part filled by new cone South flat ~150 m deep Source of >3 massive pyroclastic flow forming eruptions over last few thousand years

Cones and uplift

1988 Cones

Concentrated at edge of caldera? What is high ground to the south of the caldera?

Conclusions

Tongan volcanism Many potential eruption and tsunami sources and >12 major

eruptions over the last ~6700 years

Newly discovered Hunga Caldera Source of major ash layers on Tongatapu and beyond

What next Monitoring? Follow-up survey, detailed bathymetry, ROV? Geochemistry, more dating – correlation to ash layers