Will it Bang, Bubble, or Fizz? Shane Cronin – Massey University Anticipating the next eruption of Mt Taranaki

Clue no: 1 – what’s at the top?

Rock-falls/avalanches <1 km runout Block-and-Ash Flows (BAF) Can be 15 km runout What happens when domes fall down? Photos: G. Lube

Merapi volcano – June 2006 Twin brother of Mt Taranaki Erupting sporadically since 1994 >150 deaths June 2006, 20,000 evacuated, 2 deaths “minor eruption” evidence of it may never be recorded in the geologic record Aster Image

>700 o C “block-and-ash flows” Photos – T. Wilson

Original Channel Fill >1 year later The aftermath – rain-generated lahars

How do we know this from Taranaki?

Blue-Rata Reserve Taranaki, 15 km from source Charcoal 3 m

Example Taranaki BAF 15 km runout 2200 m drop Image T.Platz

Clue no 2: Pumice

Burrell Lapilli – AD 1655

Explosive eruptions – “Plinian” Map: T. Platz

Other types and sizes of eruption?

Eruption styles a) Sub-Plinian b) Dome a b Mineral clues – iron oxides Images: M. Turner

Clue no 3: Pulses of magma “recharge” Feldspar textures Images: Platz, Turner

A repeating pattern of eruption episodes opening pumice eruption lava-flows and dome building Repose (  degassing) next episode Episode 1 Episode 3 Episode 2

Umutekai – New Plymouth Clue no 4: Detailed eruption histories

Overall time-smoothed eruption rates Image: M.Bebbington

Sub-Plinian Dome Splitting record into two types Image: M.Bebbington

Where are we in the cycle?

Conclusions – next eruption at Mt Taranaki We are in an unusually long (although not unprecedented) lull in activity The next eruption could take one of three possible general forms: 1.Large explosive pumice eruption (last one AD1655) – not likely 2.Small explosive pumice eruption 3.Lava dome eruption Both likely types of eruption will begin with collapses from the summit area – intrusion of magma (oversteepening, earthquakes), and vent clearing Both types of eruption could herald a period of more frequent eruptions to follow A lava-dome eruption could continue for many years/decades

High Low Hazard Zone 1:300yrs 1x10 6 m 3 Risk of inundation Anticipated hazards for the start of the “next one” Image: J.N. Procter