Thursday, March 12, 2015

The magnetic and gravity surveys

The magnetic and gravity surveys: Friday 13th March 2015 – On the way to Devonport

You will recall from my earlier posts that in between Sentry deployments she requires a period of battery recharging. When Sentry is not in the water we have been running surveys assessing the magnetism of the rocks on the seafloor and variations in gravity. I thought it would be a good idea to focus a post on these surveys. Dr Fabio Caratori Tontini is in charge of these surveys, and he will assist me with this blog post.
Volcanic rocks contain the minerals magnetite and/or titianomagnetite and this enables their magnetic signatures to be measured. This is particularly useful in the case of this mission as it will tell us information about what rocks the ship is travelling over and can also provide insight into volcanic processes. We can measure the magnetism of the rocks on the seafloor by using a piece of equipment called a magnetometer (or ‘maggie’ for short) that is towed behind the ship, in our case at a distance of about 200m so that the sensor does not ‘see’ the effects of all the steel that is the ship!

Magnetometer being deployed by a Navy sailor, Fabio and Cornel
The gravitometer, as you might expect, measures variations in the Earth’s gravitational field on the seafloor. This is useful because different rocks have different densities influence the local gravity, which we can detect. Therefore, by measuring these variations in the gravity measurements we can determine information about the type of rocks that are on the seafloor and through modelling, get a good idea of their thickness. When combining these two measurements together, we can get good insight into the volcanic processes that have occurred in the past to form the volcanic edifices that are on the sea floor.

Gravitometer located in the engine room of the HMNZS Wellington
 One interesting preliminary finding here is that inside the large Macauley caldera we can see distinct magnetic and gravity ‘lows’ (see picture).  When volcanic rocks solidify, their magnetic properties (of magnetite) will lock into a single direction aligned to that of the Earth’s magnetic field at the time, hence they will all ‘point’ in the same direction. But if that material has been blown apart and redeposited with a random orientation, as would material ejected during an eruption, the corresponding previously coherent magnetic signature will effectively be cancelled out as many bits of rock will have fallen in many different directions.  Having both low magnetic and gravity anomalies therefore suggests that the material in this area is of relatively low density and the magnetism is very erratic (or demagnetised), almost certainly the consequence of a huge eruption with the collapse of the eruption column falling back down and infilling the caldera. 

maps showing the results from the gravity and magnetic surveys. Notice the orangey-browny coloured section within the gravity map and the blue area within the magnetic map indicating the centre of the caldera and material from the collapsed ash column is potentially

The gravity survey tells us that the rocks inside the caldera at Macauley volcano are of low density. This suggests that the material is not one consolidated mass. The magnetic survey shows the caldera infill material has no real magnetic anomaly. When considering these two pieces of evidence together (magnetism pointing in all directions and low density rocks) this suggests that the material at this location is likely to be unconsolidated material and not one large, dense mass of rock, such as lava. When we consider that this is the site of a volcano which we know to have erupted violently in the past we can then begin to make some interpretations about what this material could be. In all likelihood the material infilling the caldera is from the volcanic ash column after it collapsed, thereby filling the caldera caldera (see my crudely drawn image below).

Josh’s crudely drawn graphic of the potential sequence of events based on our gravity and magnetic surveys

Rescuing a sailor

Rescuing a sailor from Cyclone Pam: Friday 13th March – Mid-Kermadec Arc

Unfortunately the seas have become too rough to be able to deploy and retrieve Sentry safely both for those participating in the operation and for Sentry. Add this to the fact that Cyclone Pam is coming towards us, which has resulted in the decision to return to Auckland about one week earlier than planned.
However, we discovered a sailor anchored at Denham Bay on Raoul Island. The Navy sent a sea boat to inform him about Cyclone Pam (he had no idea) and told him that he should make a run for New Zealand immediately. For reasons unknown, he did not depart for about 5 hours and now there are questions about whether he will make it to New Zealand before the cyclone hits the area. Therefore, the Captain of the HMNZS Wellington made the decision that he would go back over to see him and ask him to join us. Fortunately, he decided to take two hours to pack up some belongings and to join us.

Captain Graham Maclean takes a sea boat to talk to the master of the yacht and ask him to join us

I thought I would take a moment to take a break from science and post about what life on the HMNZS Wellington is like, as it is quite unique.

As the blogger for the voyage, I am fortunate enough to keep friendly hours on the ship. By that I mean I usually wake up at 6.45am when the ‘wakey-wakey’ message is ‘piped’ (broadcast, and very loudly) throughout the ship. The message begins with a series of ear piercing whistles and a portion of a random song usually related to the day, or about waking up.

One of the cabins we are staying in on-board
Then it is a trip to the shower, which can be difficult to manoeuvre when the ship is rolling back and forth. Thankfully, there are hand rails to hold onto! Then off to the mess for a breakfast of champions. The breakfast options are usually: bacon, eggs, baked beans, hash browns, fruit, toast, and cereal. After an initial day or two of sea sickness, I decided it was best not to be too gluttonous and so usually just stick to a couple bits of toast.

I will usually then spend some time outside on the flight deck if the weather is nice, and for the most part it has been absolutely brilliant! As someone who has never been to sea it is quite extraordinary to look around and be completely surrounded by the ocean.

A view from the flight deck of the HMNZS Wellington)

It is then time to visit the ops room and get the latest updates on the mission from our Chief Scientist Cornel de Ronde.

The GNS Science operations room

Throughout the day the Navy run numerous drills to make sure they are always on their toes and ready to respond to any crisis. These can range from engine failure drills to firefighting drills to person overboard drills. Getting to witness these drills, I was very impressed with how quickly they can go from zero to total action! On our first day heading to sea, they ran a person overboard drill and within seconds they had deployed a sea boat to retrieve the dummy that was thrown overboard. That was quite comforting!

Sea boat being deployed during a person overboard drill

At noon it is time for lunch which usually has 2 or 3 different options available. Options include things such as chicken salad, pork wraps, pastas, salmon, and steak. Every day is something different. There is also a selection of fruits and vegetables. You certainly don’t go hungry on the ship!
Throughout the day I will pop around and have a chat to some of the others on the ship. We are fortunate enough to have a TV crew from TVNZ on board. So it is interesting to watch Renee and Mike conducting interviews while the ship is constantly rolling backwards and forwards. I am not quite sure how Mike manages to keep the camera steady, while I can barely stay on my feet through some of the close to 30 degree rolls!

Dinner begins at 5.40pm and is similar to lunch with different options available. Following dinner there is one last opportunity to venture outside before sunset, after which we are not allowed outside without permission. Usually before sunset at around 6pm we will retrieve Sentry and this is always interesting to watch. Then it is off inside for the night, and I will usually hit the hay about 9-10pm.
So that is life at sea. It is simple, but the days do pass surprisingly quickly.

Monday, March 9, 2015

Macauley Caldera

The first dive and the calm before the storm– March 8th 2015 – Macauley Caldera

We are currently located near Macauley Island, which is a small island (about 3 km2) that is part of what was a large volcano. Much of this volcano would have protruded from the ocean surface several thousand years ago. However, a large eruption about 6,300 years ago is thought to have caused much of the volcano to collapse, forming what geologists call a caldera (a collapsed volcano), and leaving just this small island above sea level. The caldera is about 9-10 km long and 5-6 km wide, which encompasses an area about the same size as Wellington harbour!).

Macauly Island from the HMNZS Wellington

At Macauley, our mission has two broad objectives. First, will be to locate all major hydrothermal vent sites within the Macauley caldera. These locations are of ecological significance, and can be sources of copper, zinc and gold mineral deposits. The second objective will be to assess what are called ‘sediment waveforms’. These are basically concentric ‘rings’ of sand that radiate outwards from the caldera flanks and which stand up to 100 m from the seafloor, becoming progressively smaller with distance from the volcano (see image below).
The purpose of mapping these features is to determine how they formed. There are currently two different ways these types of structures are thought to have formed. Firstly, by submarine landslides (or slumps), and secondly (considered more likely) by the volcanic ash column created during the caldera forming eruption hurtling into the sky then buckling under its own weight, causing it to collapse back down into the volcano and cascading into the sea. Either of these two scenarios could have potentially generated a tsunami, which means that assessing the likelihood of either scenario is an important contribution to assessing tsunami hazard in the region. By using ground penetrating sonar aboard Sentry, we can get an idea of the internal fabric of the waveforms.  For example,do the waveforms have a chaotic internal fabric, suggesting submarine landslides, or a more layered structure, indicative of collapse of the ash column?

Macauley caldera and sand waves, image created by Susan Merle of NOAA

(Macauley caldera and sand waves, image created by Susan Merle of NOAA)
We deployed Sentry for her first dive of this mission on March 7th 2015. Unfortunately, she resurfaced about 30-60 minutes after deployment due to communication issues between Sentry and the ship. In this case, as Sentry approaches the seafloor she wants to be able to “see” the seafloor; her sonar on-board was struggling to do so, so then she will obey commands in the programming to abort and come to surface, unless overridden by separate commands sent from the ship. With the communication (‘comms’ as they like to call it) problems between vehicle and ship, Sentry did not get an overriding command to keep diving and so surfaced. The good news is that on the morning of Sunday 8th March Sentry was deployed and in the evening (about 12 hrs later) she was successfully recovered! Now it is time to look at the data she collected on this first dive. About 33 GB of multibeam data alone were collected during the dive!
In other news, the weather the last couple of days has been fantastic! We have had a barbeque, passed near a huge pod of dolphins, and watched amazing sunsets.

Sunset, calm seas, and dolphins from the HMNZS Wellington

….But that is all about to change….We have had word that a large storm (potentially a category 4-5 cyclone) is heading our way. It is estimated to reach us on the weekend. This means that operations are likely to be either paused and we shelter behind Raoul Island (using it to block the brunt of the storm) until it passes, or cut and run (meaning an early return to Auckland). The first priority will be the safety of those on-board the ship. There is also the additional consideration about making sure that Sentry and any other equipment (including the ship itself) does not get damaged. Discussions are ongoing about the best strategy moving forward.

Sunday, March 8, 2015

Raoul Island

Paradise and devastation in the Pacific – Friday 6th March 2015 – Raoul Island

Today we were fortunate enough to visit Raoul Island while supplies and people were offloaded from the HMNZS Wellington. After a day of sea sickness, I was really looking forward to some nice solid land, even if it was a volcano! The fact that Raoul Island is a volcano should not be understated, it last erupted in 2006 unfortunately resulting in the death of a Department of Conservation (DoC) worker. Raoul Island is also a DoC controlled bird sanctuary. Evidence of how DoC managed to do this was seen the night before we landed on Raoul Island, as we were subjected to a rigorous quarantine and inspection process to make sure we were not bringing any seeds or unwanted creatures (e.g., rats) onto the island.
Raoul Island from the HMNZS Wellington

The day begin bright and early to make sure enough time was given to the workers getting their supplies off the ship. To get onto Raoul Island was a bit of an interesting experience to say the least! First we were transported from the ship to close to the island by a navy zodiac (basically a jet boat that gets deployed from the ship). We would then jump from the zodiac onto a smaller zodiac which would transport us up onto a rocky platform known as “Fisherman’s Rock”. We would then have to leap (without any hesitation) from the boat onto the rocky platform in between the waves which could knock us off. All that was going through my head while watching others attempt this was that I was going to be the one who would screw this up and look like an idiot. Thankfully, it went without a hitch!

Inside the Navy zodiac about to be deployed from the ship, photo from Fabio Caratori Tontini

  Our mission for the day was to head into the caldera crater to look at how things have changed from before the 2006 eruption and now. I also had the additional responsibility of filming footage for the TVNZ crew, which was also pretty cool! It was my first experience entering a volcanic crater, and my first lesson was just how tough it is to do. Steep crater walls were navigated using ropes to get down into the crater (and up to get out). 

From the inside, the crater looks like a wasteland with charred trees stripped of vegetation, and volcanic ash and bombs littering the site. Some very slight bubbling from the crater lakes could be seen due to gases being released from below, indicating that this is very much a volcano still simmering away. But it was very minor. Putting on my geologist’s hat, what struck me was the variety of rocks that could be seen in the crater. Rocks that were formed within the magma chamber prior to eruption sitting alongside rocks that at one time formed parts of the crater wall and crater lake was clear evidence the 2006 eruption was an explosive one (as if the charred trees stripped of all vegetation wasn’t a dead giveaway).

A view from within the crater, photo from Fabio Caratori Tontini

After navigating our way back out of the crater, we were fortunate enough to be invited to the accommodation for DoC volunteers and workers. A beautiful view from the deck of the accommodation out onto the Pacific Ocean was truly amazing. If the view wasn’t enough, I also tasted the best orange juice I have ever had (perhaps a bit of hyperbole due to overwhelming thirst from climbing the crater walls), squeezed from oranges taken from the 135 year old Raoul Island orange orchard.

View from the deck of the Raoul Island accommodation, photo from Fabio Caratori Tontini

Before my visit to Raoul Island, I wondered who in their right mind would want to spend up to 18 months on a tiny island in the middle of the Pacific, away from all the home comforts. I still think 18 months is a little extreme, but my view has definitely softened. I think I could do stint of a month or two in the summer time assuming no volcanic activity was being registered (I am a bit of a fair weather geologist)!
On reflection, Raoul Island really does tell two contrasting stories. First, the story of destruction from within the crater, and second the story of perhaps New Zealand’s greatest predator free sanctuary and the workers who made it happen. I think I speak for everyone in the team when I say it was a fantastic experience that none of us will ever forget.

Finally, as I write this we are planning our first actual deployment of Sentry which should be entering the water early morning on March 7. This first deployment will be shortened (about 12 hours) to make sure that all the equipment on board is operating properly.

Friday, March 6, 2015

A little yellow submarine

A little yellow submarine – Thursday 5thMarch 2015 – At sea heading towards Raoul Island

We might have departed a day late, but we are now on our way to Raoul Island! Along the way we undertook a few tests of deploying and retrieving Sentry. Some dolphins got very interested in this process and came for a visit.
Dolphins come to visit the ship
While in transit, it seems like the ideal opportunity to talk about our key piece of research equipment for the voyage – Sentry, an autonomous underwater vehicle, otherwise known as an AUV. As I mentioned in the first blog, Sentry is owned and operated by Woods Hole Oceanographic Institution (WHOI), a US based institution, and Sentry’s job is to travel to just above the sea floor and collect data related to the geology, structure and water column of (in our case) submarine volcanoes. At first this seems like a simple task, but after talking to some of the team you quickly gain an appreciation for just how complex and truly amazing Sentry is.
Sentry is worth somewhere in the range of $8 million dollars...and we are sending her to the bottom of the ocean and on top of hydrothermally active submarine volcanoes! It probably doesn’t need to be said that when dropping this sort of money into the ocean, you want to be certain that it is going to come back!! This means that Sentry needs to be able handle the high pressures associated with this depth and that it can later be retrieved from the sea surface.
Sentry out for a test deployment at Devonport Naval Base
Retrieving Sentry is no easy task. A large group of people working in sync is required to retrieve Sentry from the water. A group in a boat will first attach a line to Sentry and when this has been done a crane operator will lower the crane so that a heavier line, or strop, can be attached to the crane (pictured).  The crane then lifts Sentry from the water and once close enough, three additional tag lines will be attached by personnel on the ship to help stabilise Sentry as it is lowered onto the deck where it is secured into place in its custom-built cradle.
The retrieval process
 As an AUV, Sentry is unmanned and works essentially by itself. Basically, it gets sent down to the bottom of the ocean, does its data collection job, then when it gets runs out of battery it comes to the surface where its batteries will be recharged for the next deployment. We will be sending Sentrydown for 18 hours per dive, then recharging the batteries for 16 hours (puts my smart phone to shame). Once it is back, data can be retrieved from Sentry. In fact, Sentry’s battery pack has about 13,000 times more power than a high-end smart phone.
When we reach Raoul Island the HMNZS Wellington will be unloading Department of Conservation (DoC) workers and their huge amount of supplies.  Meanwhile, we will have a quick look around the Caldera (the crater at the summit of the island). Once this is complete, we will be heading to Macauley Caldera where we will deploy Sentry for our first dive. In the next blog I will talk about our visit to Raoul Island.

Monday, March 2, 2015

An anxious beginning

Tuesday 3rd March 2015 – Devonport Naval Base

Welcome to the submarine volcanoes blog! My name is Josh Hayes, I am a University of Canterbury post-graduate student who has the great fortune of joining this exciting research collaboration between GNS Science, Woods Hole Oceanographic Institution (WHOI) and Royal New Zealand Navy.
We are about to embark on a journey on board the New Zealand Navy vessel HMNZS Wellington to a chain of volcanoes that stretch northeastwards from the Bay of Plenty to Tonga and beyond, and commonly known as the Kermadec Arc. What we are particularly interested in is building detailed geological maps of two submarine volcanoes (Macauley and Giggenbach) and increasing our understanding on the seafloor hydrothermal systems they host (more on this in a later blog!).

To do this we will be using an awesome piece of equipment called Sentry (pictured) which is an autonomous underwater vehicle (AUV). Sentry will be deployed from the Wellington and will dive to the seafloor, where it will ‘fly’ above the rocks and sediments at an altitude of about 65 m.  It will map the bathymetry (depth and shape of the seafloor) in high resolution (about 1-2 m) as it travels across the summits and calderas of the volcanoes, collecting various types of data which can be used to build 3D maps.

We will also be stopping at Raoul Island to drop off supplies and people from the Department of Conservation (DoC). In addition, one of our scientists will spend the duration of the trip at Raoul Island to collect rock samples.  These will be useful as they provide insight into volcanic processes occurring on submarine volcanoes without the need to collect rocks from the sea floor.
We are currently docked at Devonport Naval Base while the team prepares for the trip ahead. We were scheduled for departure today, but there are delays due to a few technical issues which need to be solved. While this happens, I thought it would be a great opportunity to introduce the research team!

GNS Science
Cornel de Ronde (Chief Scientist)
Cornel is a research geologist with GNS Science. He is the Chief Scientist on this project, and has conducted a lot of research in this area of New Zealand.

Fabio Caratori Tontini

Fabio is a marine geophysicist with GNS Science and will be running the regional gravity and magnetic surveys of the sea floor when Sentry is back aboard the Wellington.

Christian TImm

Christian is a petrologist with GNS Science. We will be dropping Christian at Raoul Island where he will be collecting rock samples.

Arran Murch

Arran is a PhD student at University of Otago studying explosive submarine volcanism. Arran will be assisting Fabio with running the magnetic surveys.

National Oceanic and Atmosphere Administration (NOAA)
Sharon Walker
Sharon is an oceanographer with NOAA. Sharon researches chemical and biological changes in the water column to help zero in on the location of hydrothermal systems.

Carl Kaiser is the operations manager of Sentry. He will be in charge of running Sentry’s trips to the sea floor. Carl has a group of engineers (Andy, Justin, Sean, Zach) working alongside him who will be assisting with deployment and recovery of Sentry.
This will be an absolutely fantastic research journey, and I look forward to providing updates on this blog!
That is all for now. Tomorrow we depart!!!

Sentry AUV. Image from Carl Kaiser.

Wednesday, February 25, 2015

Submarine volcanoes

Josh Hayes is normally a post-graduate earth science student at Canterbury University. He has taken a breather from uni to travel to the KermadecArc to report on some exciting research on submarine volcanoes. In this blog, he provides a bird's eye view of a joint project involving GNS Science, & Woods Hole Oceanographic Institution (WHOI), and the Royal New Zealand Navy. His reports are coming direct from HMNZS Wellington, which is currently northeast of New Zealand.