Background - Past natural disasters in the Bay of Plenty

Quicklinks

The 1886 Tarawera eruption Edgecumbe earthquake Historical tsunamis

Since European settlement of the Bay in the mid-Nineteenth century, several natural disasters have occurred. These events serve to clearly illustrate the range and scale of potential hazards to the people and property of the Bay. Below is a summary of some of these disasters.

The 1886 Tarawera eruption

• This eruption occurred on the 10th of June 1886, and involved a series of eruptions in the Lake Rotomahana and Lake Tarawera area.
• The eruption column rose to an estimated height of 9.5km, and was recorded by ships 220km away.
• The eruption is remembered for the loss of approximately 108 lives and destruction of the renowned "Pink and White Terraces".
• At total volume of 1.3km³ of basalt ash and lapilli and Rotomahana Mud ejecta is estimated to have been expelled during the eruption.
• Ash and other ejecta from the eruptions were estimated at the time to have covered 15,000km², but the majority of this deposit was washed away. Today, the remaining ash from the Tarawera eruption covers 4500km² at up to 5cm thickness.

Old Mill at Te Wairoa (ca 1886). By permission of the Alexander Turnbull Library, Wellington, New Zealand.
Permission of the Library must be obtained before any re-use of this image.

Isopach map of the area affected by the 1886 Tarawera Rift eruption. Compiled by Professor A.P. Thomas in July 1887.

top

Edgecumbe earthquake

At 1:42pm on the 2nd of March 1987, a magnitude 6.3 earthquake struck the town of Edgecumbe in the eastern Bay of Plenty. The earthquake epicentre was approximately 8km north of Edgecumbe and, while there was no loss of life, there were significant physical impacts and social disruption.

Physical impacts:

• A giant fissure (surficial break) up to 3m wide, 3-4m deep and 7km long opened on the Rangitaiki Plains. This was later identified as the Edgecumbe Fault.
• The entire area was twisted slightly, resulting in the hills east of the Rangitaiki Plains moving 0.6m southwards.
• Land on the northwestern side of the Edgecumbe Fault dropped by 2m. On the northwestern side of the Awaiti Fault land dropped by 1m, and much of the Rangitaiki Plains dropped.
• Liquefaction was common along river banks and paddocks of the Rangitaiki Plains.
• Sand was brought to the surface by ground shaking, resulting in sand blows.
• Ground shaking also caused landslides and slumps in the hills.

Social disruption:

• Infrastructure was damaged with power, water, sewerage and telephones cut in many areas. Railway lines and roads were either damaged or blocked by landslides.
• Significant damage to local industry and businesses, with the temporary closure of factories and shops affecting 3180 employees.
• Farmland was also affected, with damage to river stopbanks and paddocks where fissures and faulting occurred.
• 3000 people were evacuated from the area south of the Matahina hydro dam in case it gave way.
• Local schools were closed for 15 days.

top

Historical tsunamis

Tsunamis are thought to be relatively common around the New Zealand coast with an average of 12-13 events exceeding 1m wave height occurring every century. Since 1840, 12 tsunamis have been recorded along the Bay of Plenty and Eastern Coromandel coastline (Bell et al., 2004). The largest tsunamis to have affected the region through this time have been generated by "distant" sources, with the three largest (1868, 1877, 1960) all generated by large earthquakes in the subduction zone along Chile and southern Peru coasts. (Bell et al., 2004; de Lange, 2003).

The 1868 Peru tsunami was generated by a magnitude ~9 earthquake off southern Peru and northern Chile. Some of the known effects within the Bay of Plenty were:

• At Port Charles houses inundated to a depth of approx. 0.6m and a tramway was washed away, along with boats and stacked timber.
• Bores at Maketu, Opotiki, Opepe, and Torere.
• The wave swept about 20m inland in Huruhi Harbour, Mercury Island.
• At Raukokore, near Cape Runaway the tsunami damaged boats and swept canoes, boats and timber out to sea (Bell et al., 2004).

The 1877 Chile tsunami was triggered by a magnitude ~9 earthquake off northern Chile. Damage within the Bay of Plenty thought to be less than in 1868, however the tsunami is known to have:

• Damaged the wharf, washed away logs, and inundated the flat area and houses at Port Charles.
• Caused vessels to drag anchors and a fence to be washed away on Mercury Island.
• Flooded beach houses at Tauraunga (Bell et al., 2004).

The 1960 Chile tsunami is the largest recorded tsunami in NZ. This was triggered by a magnitude 9.0-9.5 earthquake off central Chile. The tsunami run-up in Chile was estimated to be up to 25m, and run-ups over 6m were recorded in Japan and Hawaii. In the Bay of Plenty region the recorded effects were:

• Estimated run-up of between 0.5-3m, with oscillations at Mercury Bay recorded up to four days after the initial event.
• The tsunami was recorded in Whitianga, Mercury Cove and Bay, Mount Maunganui, Tauranga, Kaituna River, Maketu, Whakatane, Ohiwa Harbour, and Opotiki.
• With the associated drawdown deep water sandbanks were exposed at Mercury Cove, as was the wreck of the Buffalo at Whitianga.
• At Whitiagnga and Maketu boats were swept from moorings.
• Significant erosion was noted at Maketu and Ohiwa Harbour.
• At Whitianga tsunami waves inundated roads and the airport and flooded several houses (Bell et al., 2004).

top

Further Reading

de Lange, W.P. 2003. Tsunami and storm-surge hazards in New Zealand. In: The New Zealand Coast: Te Tai O Aotearoa, Goff, J.R.; Nichol, S.L.; Rouse, H.L. Dunmore Press, Palmerston North. p. 79-95.

Bell, R.G.; Goff, J.; Downes, G.; Berryman, K.; Walters, R.A.; Chaugé-Goff, C.; Barnes, P.; and Wright, I., 2004. Tsunami hazard for the Bay of Plenty and eastern Coromandel Peninsula. Report to Environment Bay of Plenty and Environment Waikato. Hamilton, New Zealand. NIWA. (see http://www.envbop.govt.nz).