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Table 1 Scale of Ruapehu eruptions after Scott (2013)

From: Phreatic eruptions at crater lakes: occurrence statistics and probabilistic hazard forecast

Eruption scale

Observed effects

0

Crater Lake steaming, hotter than normal (i.e. above 30-35 °C) creating additional interest, but no observations (or confirmation) of activity in lake.

1

Small phreatic eruptions, confined to Crater Lake.

2

Phreatic or phreatomagmatic eruption accompanied by surges; material deposited outside Crater Lake, but still confined to the crater basin. May produce larger flows/floods in Whangaehu Valley.

3

Deposition of material outside the crater basin; possible remobilisation/lahars in upper catchments and Whangaehu valley; OR small scale explosive eruption/intermittent ash emission when no lake is present.

4

Material deposited well outside the crater basin onto the summit plateau and outer flanks. Lahars possible in several catchments; OR explosive ash eruptions when no lake is present producing columns up to 10000 ft (about 3 km).

5

Large scale explosive eruption displacing moderate volumes of the lake, lahars in all/most major valleys. The summit and slopes covered with ashfall off the cone; OR explosive eruptions when no lake is present producing tall (> 10000 ft (about 3 km)) eruption columns and ashfall off the cone.