hunga ha’apai-hunga tonga – birth of a new volcano and...
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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
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