Island Hopping: ATom Style!

Ascension Island, 1600km west of Africa, 2250km east of Brazil, and 1300km north west of its closest neighbor, St Helena (population around 4000) is rather remote. It’s also rather young, having been formed by volcanic activity just a million years ago. We’re grateful that it was, since it provides us with a strategic place to land part way up the Atlantic while sampling very remote air. It was claimed by the British in 1815 when Napoleon I was exiled on St Helena, with a view to preventing anyone from using it as a base from which to rescue him. Nowadays it remains a British Overseas Territory, with both British and US military bases and a population of about 900, mostly from the UK and St Helena.

Map of Ascension Island By Ile_de_l'ascension.svg: Treehillderivative work: Treehill (fr) Treehill - Ile_de_l'ascension.svgMap for free, CC BY 3.0,
Map of Ascension Island By Ile_de_l’ascension.svg: Treehillderivative work: Treehill (fr) Treehill – Ile_de_l’ascension.svgMap for free, CC BY 3.0,


Georgetown, Capital of Ascension Island
View of Georgetown, Capital of Ascension Island, from Cross Hill (credit: Christina Williamson)

I was therefore quite pleased that my instruments were all performing well and not needing much attention, so that after processing and checking my data I had a little time to explore this unique place.

The island is mostly volcanic rock, and very barren, with lots of peaks of various sizes. In 1850 the botanist/ explorer Joseph Hooker decided to plant a bunch of tree on the highest peak. With steady trade winds crossing the island this creates its own micro climate. This captures the rain and improves soil quality, allowing more plants to grow and transforming this part of the previously barren island into a rain forest. It has aptly been named Green Mountain.

Green Mountain on Ascension Island (credit: Christina Williamson)
Green Mountain on Ascension Island (credit: Christina Williamson)

We rented cars from the hotel on the island (in-fact, we rented every single car available for rent on the island – not a huge number of them). A group of us headed up green mountain. Most of the roads are narrow, single-track affairs, which works out fine since you rarely meet anyone coming the other direction. In-fact it is a custom on the island to smile and wave at everyone you see, I guess because when there are so few humans, it’s quite a pleasure to run into one. You’re much more likely to run into a donkey, sheep or goat, which roam wild on the island – so much so that there’s a hefty fine for hitting one with a vehicle. We were also told to be careful not to run over any land crabs, which wander about the place.

Feral donkeys on Ascension Island (credit: Christina Williamson)
Feral donkeys on Ascension Island (credit: Christina Williamson)

As we ascended green mountain it we drove cautiously, not only because of all of the animals we needed to avoid, but because the road was incredibly steep and windy, with hairpin bends on a steep camber, and we were driving a rather old manual pick-up truck, with a gear stick that would often come apart as you tried to change gear. Reaching the top of the road was something of a relief, not just from the heat, but from the drive (temporarily ignoring the unpleasant fact that what goes up must come down, which would prove even more nerve wracking).

Originally the British had tried to build a settlement up here as the climate is much cooler and there is fresh water to collect, but it proved so damp that disease set-in and they decided to move it back down. There were a number of deserted buildings up there, as well a concreted over hill-sides for water collection. They maintain a good series of paths up there for walking, and we did a short hike, admiring the views. The humidity up there provides a better climate for animals as well as plants. This includes a large population of rats (which presumably arrived here on the ships). I have a severe aversion to rats, and we decided to head back down after one too many encounters with them. I was very relieved to be away from them, and to have made it down the mountain without careering over the edge of a hairpin bend.

We visited a few beaches and coves (it’s easy to see a lot of this island in a short amount of time, since it’s only about 6 miles across). The ocean is teaming with life here, and we could see scores of sea turtles swimming just off shore, and fish and eels closer in. Most places on the island are far too dangerous for swimming, with big rip currents, sharp volcanic rock (name) that will cut and infect you very easily, rouge waves the can be up to the 30m tall (and the non-rouge ones are pretty big too), oh and sharks, in-case you need further dissuasion.

Comfortless Cove in Ascension Island (credit: Christina Williamson)
Comfortless Cove in Ascension Island (credit: Christina Williamson)
Waves on Long Beach, Ascension Island (credit: Christina Williamson)
Waves on Long Beach, Ascension Island (credit: Christina Williamson)

However, there are two beaches on the island where it’s deemed safer to swim as there are at least no rip currents and a sandy beach in between the volcanic rock. We visited one of these and the base commander informed us that the sharks were mostly not interested in humans, and the eels would only attack you if you come too close to them while they’re out of their holes. So we went for a swim. The waves were big and pounding and the water pretty warm. It felt great to be in the water, and lovely to see other scientists and crew, who are all working so hard on this mission, take a moment to relax and play at hurling themselves into the waves.

We also saw an amazing blow hole at the northern tip of the island. It was beautiful to watch the waves crashing in with such power. Networks of holes in the volcanic rock would allow for what looked like isolated pool to fill and empty from below with the larger waves, and we found a crack in the rock that would hiss and gurgle.

Blow hole on the northwest tip of Ascension Island (credit: Christina Williamson)
Blow hole on the northwest tip of Ascension Island (credit: Christina Williamson)

In the evening, after it had got dark. A few of us went down to the beach with a small red headlamp. Its peak season for the green sea-turtles to lay their eggs. The come up to the beaches at night, dig holes in the sand (so the beaches during the day are all cratered). You have to be very careful not to disturb them, especially as they’re coming up the beach, as they might turn back if they don’t feel safe. However, once they’re settled in and digging, you can watch from a distance (hence the red light, which doesn’t disturb them as a white one would). It’s incredible. The beach was dotted all over with these amazing creatures digging away. They’re big: about 1.5m long, and have very articulate back flippers, which they use to scope out the sand and form very circular holes, a good meter in depth sometimes. This is pretty hard work. It’s easier to find the turtles by listening in the dark than with the dim red light. You hear the sand been thrown out of the hole in a few scoops, followed by a deep sigh and some heavy breathing, before the turtle goes at it again. The stars were also beautiful, as there is so little light pollution out here.

Craters in the sand on Ascension Island made by sea-turtles for laying their eggs (credit: Christina Williamson)
Craters in the sand on Ascension Island made by sea-turtles for laying their eggs (credit: Christina Williamson)

The stars were still beautiful at 5:30am as we headed back to the plane for pre-flight. There’s practically no diurnal cycle in temperature on Ascension, it was basically flat around 30C the whole time we were there, and we had no air conditioning cart for the aircraft. For many of us, this proves difficult as we need to try and keep our instruments from overheating. I did a staggered warm up, leaving the instruments that are sensitive to temperature until the last moment to switch on, which worked relatively well.

We were flying on to Terceira Island, in the Azores. This is a shorter distance than we had to do on the last two legs, so we were able to make more vertical profiles, 7 in total, not counting the ascent and descent on take-off and landing. There’s a lot going on in this region, crossing the ITCZ, biomass burning and dust influences from Africa, areas of strong convection, so we were all happy to be able to sample so much of it. As we passed low over the ocean we occasionally saw streaks or circles of orange in the water, which were algal plumes.

We arrived in Terceira late in the afternoon. For two small, volcanic islands in the middle of the Atlantic (albeit very far away from each other) they could hardly be more different. Coming in to land, Terceira appear as a patchwork of shades of green, which on closer inspection turned out to be field of cows separated by dry stone walls. Dotted about the island are little towns and villages full of churches, narrow cobble-stoned streets and houses with white walls, terracotta roofs and brightly coloured stone work. Such a contrast Ascension – we were excited to explore!

View of Ascension Island as we came in to land on the DC8 (credit: Christina Williamson).
View of Terceira in the Azores as we came in to land on the DC8 (credit: Christina Williamson).




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