Raoul Island and the other Kermadec islands are the summits of large volcanos that have been built up on the Kermadec Ridge. This ridge lies along the collision zone of two major structural plates, the Pacific plate to the east and the Australian plate to the west. The Pacific plate is being forced beneath the Australian plate, thus causing the characteristic deep ocean trenches that surround these islands. The movement of these plates has been estimated to occur at a rate of about 7cm per year on average and the earthquakes commonly felt in this area are likely to be associated with the convergence of these plates.*( Volcanic Hazards–MINISTRY OF CIVIL DEFENCE –Information booklet 4,1992).
The island has been shaped by its explosive history. It consists of two main craters or calderas which have been formed due to subsidences immediately after large eruptions. The Raoul Caldera centrally is 3km by 2km and the Denham Bay Caldera approximately 3km long and wide, but this had been flooded by the sea.
Witnessed volcanic eruptions on Raoul have occurred in 1814, 1870, 1964 and 2006. Future volcanic activity and earthquake activity is likely and this is now being more closely monitored on Raoul Island and at other sites along the Kermadec Ridge. GNS (Geological and Nuclear Science) have recently installed new monitoring equipment to assist with the monitoring.
Crater vegetation damaged in the 2006 eruption
For example, a web camera looks down into the crater located from the top of Moumoukai, the highest point of the island, so you can see what the crater looks like twice each daylight hour if you click here. Seismic and temperature measuring devices are located in the Raoul crater and other devices to monitor tsunami activity are installed around the coastline. This information is monitored 24 hours a day back in New Zealand.
Protocols are in place for evacuation in the event of an earthquake or volcanic eruption. We practised an evacuation drill last week.
Emergency evacuation practice
We all packed warm clothes, tents, sleeping bags and gathered up the emergency bins containing such things as the portable generator, chain saws, fuel, food, water, satellite phones and flares.
Duties like our weeding involve searches of most of the island, including the crater. Prior to us entering the crater, John (our team leader) makes contact with GNS in order to obtain a permit to enter it. The GNS team back in New Zealand will only issue this permit if they are satisfied that their instruments show the volcano to be inactive. When we go into the crater either as individuals or in groups, a radio is always carried and we make scheduled radio contact daily at 1000 and 1500 hrs to advise of our position and well being. Weeding in the crater is pretty much like everywhere else on the island (steep hillsides, deep ravines, bluffs and huge windfall Pohutakawas to skirt around) except for the fumeroles. These are deep vent holes and care always has to be taken to look where you put your feet.
This fumerole was found while weeding last week. It was 40cm in diameter and at least 5 metres deep.
Earthquakes and eruptions cannot be predicted. We don’t spend our days worrying about these events but instead make a conscious effort to marvel and revel in our spectacular surrounds.
Also it helps to know that if shit happens, we are as prepared for it as we can be.