2015 in Review: Mostly Harmless

Our scientists are now back in the office and have finished reviewing 2015. We can now confirm that 2015 was mostly harmless. Sure, we had some wobbles (thanks Wilberforce!), and Ngauruhoe woke up a bit…then promptly went back to sleep. Overall, it was a pretty quiet year. Don’t get us wrong, we aren’t complaining…we like quieter years! Quieter years give us a chance to catch up on research, strengthen our monitoring network, install new equipment and have lunch with Leanne from accounts. One exception was our landslide team, who were kept busy with the effects of Cyclone Pam, earthquakes AND a volcano causing havoc. 

Here is the breakdown of 2015… in terms of geological action for New Zealand.

Volcanoes: Turned down in 2015 but still on “simmer”

Like 2014, volcanic activity was relatively minor in 2015. We had a burst of seismic activity at Ngauruhoe in March but by the end of April, it had gone back to sleep. In August, low gas emissions and seismic activity pulled Mt. Tongariro’s alert level down to 0 on the Volcanic Alert Level (VAL) scale. This was the first time since before the eruptions in 2012 that the level has been back to 0. White Island continued to puff and splutter away, with typical hydrothermal activity and periods of increased tremor continuing throughout the year, but no eruptions.  All other volcanoes were quiet. Mt. Ruapehu’s Crater Lake experienced high and low temperatures and a snow and ice avalanche entering and temporarily cooling down areas of the lake by a few degrees. 

What 2016 will bring is unknown but the GeoNet monitoring team continues to keep a close eye on New Zealand volcanoes.

Earthquakes: South Island dominates in Quake Stakes

2015 had a shaky start, with the magnitude 6.0 Wilberforce Earthquake. The South Island continued to dominate in the larger earthquakes stakes, with 6.2 earthquake between Kaikoura and St. Arnaud in late April. The South Island continued to rumble when the 5.8 Matukituki quake, near Wanaka, struck a week later. Fortunately, no major injuries or damage was reported from any of the quakes.

After May, New Zealand quieted down, with no major earthquakes (more than a 6.0) reported for the rest of the year. As far as the bigger quakes this year, overall, there were 43 quakes that measured more than 5.0. 31 of those 43 were far offshore, in the Kermadec Islands. The North Island was relatively quiet in 2015, with three quakes more than magnitude 5.0 striking on land while the South Island had double this number, with six in 2015.

Generally, 2015 turned out to be quieter than 2014. Total quakes this year was 20,008, which was slightly less than 2014, which had 20,711.

So what does this mean for 2016? Unfortunately, there is no crystal ball to tell us what our Shaky Isles will do next.

Landslides: Triple Threats

This year, our landslide team had a full plate with landslides caused by earthquakes, massive storms and volcanoes. We had three magnitude 6.0 earthquakes this year, as discussed in the previous section, that triggered landslides and slips in their respective areas.

But the serious action came this year from massive storms, including Tropical Cyclone Pam. Pam wasn’t the only storm to grace our shores this year with large storm and rain systems, which created considerable sized floods in the Manawatu region, also generated the largest landslides and slips. We also responded to the rainstorm that affected the Hutt Valley and Kapiti coast in May. 

Interestingly, this year, we also had a landslide caused by a volcano! White Island’s activity generated a landslide which required further investigation. 

2015 was a busy year but we were fortunate that no one was injured as the land continued to slip and slide away.    

Slow-slip earthquakes: when the earth moves very slowly

In 2015, our slow-slip earthquakes didn’t prove very exciting, as there were two slow-slip events that went on without any acknowledgement.

In Manawatu, a slow-slip earthquake started in mid-2014 and continued for the first half of 2015. Land around Manawatu moved up to 15cm to the east, which is about the length of a Crunchie bar.

In June of 2015 there was also a small slow-slip earthquake offshore of Gisborne. Land in this area is very slowly being pushed west by the colliding tectonic plates. However, land movement reversed direction for around a month and our stations moved 5-10 cm to the east. The amount of movement pales in comparison to the previous slow-slip earthquake in the area, where land moved up to 30 cm. This pattern of large slow-slip earthquakes interspersed by one or two smaller ones is a constant pattern for this area since these were discovered in the early 2000s.

Tsunami: long distance water hug from Chile

GeoNet responded to one tsunami last year – generated by a magnitude 8.3 earthquake off the coast of Chile. The tsunami experts panel estimated wave heights between 0.2-1m for much of the East Coast and the Chatham Islands, necessitating the Ministry of Civil Defence and Emergency Management to issue a beach and marine threat, that was in place for nearly 24 hours.

The resulting tsunami was consistent with the panel’s estimates, with the Chatham Islands receiving the largest wave heights – close to 1m. The maximum tsunami height on the East Coast of the mainland was closer to 50cm. Although 50cm doesn’t sound like much, it’s important to remember this is not a single wave, but a surge of water travelling faster than we can run.

In summary, thanks for the affection, Chile, but we’d prefer no more water hugs from you. While we are at it, we don’t want any from you either, Hikurangi Subduction Zone.

Best cam shot of the year:

 

And that’s it! 2015 was a quieter year than the year before…but we like quiet years. But just because 2015 was quieter, it does not mean that 2016 will be the same. 

 

Here are a few helpful places to get more info about preparing for emergencies:

  • Get Ready, Get Thru (Ministry of Civil Defence and Emergency Management)
  • Get earthquake ready (EQC)
  • Live on the East Coast of the North Island? Check out the new East Coast Lab...it's all about earthquakes, tsunami, and what you can do to prepare on the East Coast of the North Island

 

 

 

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