Tech Tales: One of our most important tsunami gauges just got an upgrade!

Published: Fri Aug 10 2018 4:30 PM

Every 10 years or so we upgrade our network of tsunami gauges (pressure sensor sites). Recently it was time for our North Cape site to receive its upgrade and so we sent the best technicians for the job, Conrad and Dave.

GNS senior scientist and tsunami expert Dr William Power says that our North Cape sensor is one of our most important sites because of its location at the northern extremity of New Zealand. Tsunamis originating from New Caledonia, Vanuatu and the Solomon Islands often make their first landfall in New Zealand in this area, and consequently data from this gauge is very useful for confirming and calibrating our forecasts before these tsunamis reach other regions of the country.

Map showing location of our North Cape pressure sensor

Map showing location of our North Cape pressure sensor

The North Cape gauge has also proved useful for our scientific understanding of earthquakes and volcanic events along the Kermadec Trench, for example this event from late last year. So it’s fair to say that keeping this sensor in top working order is a priority for GeoNet.

A lot of planning is involved in these upgrades, especially when the site is as remote as this one; you can’t simply pop back to the storeroom for more supplies. Our technicians order, organise and package up all needed supplies and freight them to the local departure point to arrive before they get there.

The North Cape site, on a small island just off the cape, is very remote and it’s not somewhere you can just drive to. Once all the gear and supplies were loaded onto the boat (including a lot of delectable BBQ food), along with our technicians Conrad and Dave and the divers, the 20-hour journey north began. The boat took off in the afternoon and had arrived at the destination early the next morning.

Boat in the bay

Boat in the bay

The rousing smell of bacon and eggs on the barbie set the techs up for the day, and they assisted the divers in removing the old cabling and sensors from the sea-floor. It is quite a job doing this because our cables are covered in heavy, protective armour that needs to be taken off along the way. We need the armour on the cables for a few reasons: to weigh the cables down so they sit on the sea-floor, to protect against nibbles from wildlife, and to protect against anything falling on them, such as rock.

The first day was spent removing all the old equipment and setting up the new data loggers on land. Our cabinets (that house our data loggers) and solar panels need to be up somewhere high and exposed so that they have a clear area to transmit the data back to us and so that it’s nice and sunny to charge up the solar panels. It’s also quite important to have the cabinet located somewhere that won’t get drowned in a tsunami. The cabinet in this location is a real mission to get to so the techs had their work cut out for them there!

The view from up at the cabinet

The view from up at the cabinet

After the first day’s work was done, the crew all had a go at fishing off the back of the boat, some had better success than others. Conrad’s line had a bite from something “massive” and it took off, snapping the line. He concedes that a better fisherman would have been able to reel that one in. The techs also took a bit of drone footage of the area for us to enjoy (and get jealous over!).

Divers with the new cable and protective armour

Divers with the new cable and protective armour

Day two saw our techs and divers installing all the new equipment, feeding the new cabling through the armour and getting the two new pressure sensors in place. Our tsunami gauge data is collected by two pressure sensors at each station so that we have a backup in case one fails. They work by recording sea level variations by calculating pressure changes compared to a baseline value. You can see where our other tsunami gauges are on our network map (they are called ‘pressure sensors’ on the legend).

The trip was a success, with the sensors performing exactly as they should, and great weather that meant the mission was uninterrupted. The techs reported great food, smooth sailing and a picturesque setting, some would say it’s the ultimate day job!