Ambrym Volcano’s Lava Lakes: A decade of fiery Geology

Ambrym Volcano is a remarkable wonder. Two imposing cones rise within a desert-like caldera and where molten lakes of lava churn within their depths. For the past decade, I’ve explored, studied and documented Ambrym volcano across 15 expeditions. It’s a notoriously difficult place to get to and equally difficult to survive once there. And it’s a volcano that has gone through unprecedented change. In this video, I document the fiery geology and unprecedented change of Ambrym Volcano.

Ambrym is a shield volcano with a large basaltic caldera at its summit – in fact one of the largest basaltic shield calderas on earth. The volcano has had the highest sulfur dioxide (SO2) emissions of any volcano over the past decade. Visually, it is a remarkable volcano. Prior to 2018, the volcano had multiple persistent lava lakes unlike anything else on the planet. One was the size of the two football fields and sat at the bottom of a crater 500 meters deep.

But then it all changed. In late 2018, I started to notice that Ambrym was restless. Seismicity increased, the lava lakes started rising and new lava lakes formed rapidly. As I pondered these unusual changes, little did I know that just a few days later, unprecedented geological events would unfold that would completely transform Ambrym Volcano and disappointedly bring about the destruction of the famed lava lakes.

On Dec 15, 2018, the lava lakes which had been persistently present for decades, drained suddenly. A few hours later, an intra-caldera fissure eruption occurred producing impressive fire fountaining and lasting approximately four hours. It produced a small cone and lava flows which can be seen on satellite. There was also nearby degassing from the existing Lewolembwi crater.

On Dec 16 large eruptions from both Marum and Benbow cones followed producing ash plumes to 8km high. With the lava draining away, large voids caused massive ground deformation and subsidence. A day after, and 20km’s away, huge fractures began to cut through the ground. The small village of Pamal was split in half. One side had risen over 2 meters high. Surrounding coastal seafloor had also been uplifted by 2 meters creating new land and leaving marine life stranded.

Large exclusion zones were set up around the fractures, fearing lava could break through at any moment. But the lava never surfaced here. Instead, days later, large pumice deposits washed up on shore. Locals told us they had witnessed red and steaming patches out in the ocean. We even chartered a small boat in search of these, but found nothing. In the weeks following, the caldera area at the summit of Ambrym was left unrecognisable.

So let’s explore the geological process that unfolded here – why we saw the draining of lava lakes, fissure eruptions, large fractures, ground uplift and pumice deposits.

What unfolded in 2018 was the result of tectonically induced stresses. The process commenced with an initial shallow dike intrusion which then triggered a larger flank intrusion resulting in the rapid migration of magma along the East rift zone – over 20km to the SE coast of Ambrym. The partial collapses of Marum and Benbow were the result of subsidence from the removal of the shallow magmatic system beneath each cone. All up about 14 billion cubic feet of magma migrated in total.

Shortly before the lave lakes drained, a series of magnitude 5 earthquake’s struck. This marked the point at which the magma began to migrate along the east rift zone. The first evidence of this easterly migration was the brief fissure eruption and nearby degassing of the Lewolembwi crater approximately 2km east of Marum cone. Over the next two days, seismicity began to also migrate further east and towards the south-east end of island (near the village of Ulei). Ground measurements also showed evidence of an easterly shifting inflation.

On Dec 17, the magma had traveled over 20km and then continued its movement beyond land to the ocean. Seismicity decreased relatively quickly thereafter. It was assumed that the magma had stopped its migration and lava was finally released through a submarine eruption as large pumice deposits washed up on shore in the days after.

Five years have now passed and Ambrym Volcano continues to evolve and change dramatically. I’ve been back every year since and have documented my observations of both the Marum and Benbow cones. Marum is the largest cone and was home to the largest persistent lava lake and a smaller semi-persistent lava pond within the Mbwelesu crater. Marum has two additional craters to the south. A collapse pit named Niri Mbwelesu (Taten) and a smaller crater Niri Mbwelesu that formed in 1989. It had laid dormant for some time until 2017 when I observed strombolian activity. It went onto develop a large lava lake in early 2018. Benbow is the second cone and had two persistent lava lakes. One large one and another named “Son of Benbow”. 

Overview of Benbow

Whilst Benbow cone wasn’t as deep, nor as massive as Marum, it is where the changes have been the most dramatic. Its crater was approximately 300 meters deep and featured an inner tephra wall that supported a large, completely flat ash plain or plateau. Often the crater would be a swirling mess of gases. During heavy rainfall it form hundreds of mini waterfalls. But it was at night when things became really magical. The entire sky would glow a hue of orange. We spent many nights camping in this area and it was undoubtedly one of the most incredible spots on the planet.

I have so many incredible memories of Benbow. The very first time I entered the volcano was on foot. We were near the top of the cone, peering into the crater which was shrouded in fog and gas. It was just getting dark and all we could see was an orange glow at the bottom. It looked terrifying. John, our local guide had fashioned walking poles from sticks out of the jungle. He looked at us and said ‘we go down”. And so without any rope or gear, we carefully made our way down a very steep crater wall to the lava lake. If you wanted to go any further, specialised rigging equipment was required. In 2015 and with the help of Geoff Mackley, we had one of our most daring expeditions to date. We made our way right to the crater floor and just meters away from the lava lake. It was an incredibly risky undertaking descending 300 meters down inside a volcano…and if we had fallen, we’d would have been swallowed up by a churning lava lake. Whilst most of our visits were on foot, other times we’d fly in via helicopter.

Benbow had two lava lakes. The main one was incredible and would churn and pulse lava 50 meters or higher at times. The second smaller one and had a circular, very narrow shaft that funnelled copious amounts of SO2. It was very hard to get to we only visited in a couple of occasions. On one trip, I dropped a go pro tethered to some steel wire and was the first person to capture views of it.

In 2018, Benbow went through a dramatic transformation. The lava lake started draining rapidly and then the crater floor suffered catastrophic subsidence and partial crater collapse. It produced large ash plumes reaching over 8km high. From a distance, the cone looks unchanged, but once you reach the summit and peer down inside the crater, it’s no longer recognisable. The inner tephra ring has collapsed. There have been massive landslides of the crater walls. The crater is half the depth of what is was and the lava lakes are buried under tonnes of debris. There is vigorous fumarolic degassing. A giant water course has opened up has started eating into the plateau where we used to camp.

Fast forward to today and we see even more dramatic changes. Most striking is that Benbow’s crater has turned green. Gas emissions are a fraction of what they were and this has enabled plant life to establish and flourish. Insects are everywhere. The plateau we camped on has been ravaged by erosion. Eventually it will collapse entirely. More landslides have occurred, further burying the the lava lakes. But in the distance, we finally have confirmation that Benbow has recently sprung back to life. A new cone has been built and fresh lava flows line the crater floor. This is the first observation and footage of this new cone. On Jan 25th 2022,just after 5:00AM local time, an eruption took place in Benbow crater, producing a plume to 1.8km. Further eruptions followed, with local villagers hearing loud explosions. At around 2:30PM, heightened seismicity was detected and a larger ash plume observed at Benbow crater. The eruption was however short lived, lasting just a few days.

Benbow’s new cone

Overview of Marum

The Marum cone is the larger of the two and was home to Ambrym’s largest lava lake in its Mbwelesu crater. At times, the lava lake swelled to three football fields in size.  I spent many weeks on the volcano’s summit, camping right beside the crater edge. The crater was absolutely colossal, and was approximately 500 meters deep. Smaller, lava ponds were present, but were never persistent. Getting to Marum’s crater floor was a huge undertaking, but we succeeded. Repelling 500 meters down and then back up whilst dodging countless falling rocks was one of the most physically demanding things I’ve ever done. We even led a Google Map expedition that took the Streetview Trekker down and captured the entire descent in full HD. It’s available on Google Maps.

What happened on Marum was particularly frightening. Our (now former) campsite had collapsed deep inside the crater.

Our (former) campsite before and after the 2018 geologic events showing the land under our tents completely gone. We had camped here for many nights, none of us knew just how precarious that spot was.

Marum also suffered suffered catastrophic subsidence and partial crater collapse. The crater is barely 2-300 meters deep now (from it’s original 500 meters).

Now unfortunately, I don’t have any recent footage of Marum and for a very good reason. The normal route was destroyed and impassable after the 2018 eruption. I tried my best to get there, but the cone flank was covered in a super slippery mud. It was far too dangerous. Additionally, the original route led us through a narrow gap between Niri Mbwelesu, and Niri Mbwelesu Taten. During the eruption, the Niri Mbwelesu Taten collapse pit expanded massively and made the passage even narrower. Erosion has basically cut it off entirely. There may be a way further south, but I haven’t had the time to investigate that either. Fog and terrible weather has stopped my from flying the drone there also. At this stage, the only way to visit Marum now is from the North (via a boat to Ranvetlam)

So what has happened in this crater? This satellite imagery does paint an similar “greenification” as seen on Benbow – and like Benbow, there has been a lava emitted post 2018 events from within the western part of the crater. Based on satellite data, it likely erupted in early 2020, well before Benbow’s last eruption in 2022.

Just south of the Mbwelesu crater is Niri Mbwelesu. This crater went through an incredible transformation in a short space of time just before the 2018 eruption. 

I had visited this crater many times, but it was always just smouldering away silently. Then in Jan 2018, as I was on my way to the Marum campsite, I heard large rumbling sounds. So I detoured and was quite shocked to see new vents had opened up producing strombolian eruptions. This activity was unusual for this crater. We came back the next day and just as I was setting up my drone, ash started being ejected and soon erupted a small ash cloud that had us running.

Over the year, more thermal readings were recorded and then in Dec of 2018, not long before the major geological events unfolded, we returned to find a massive lava lake had formed. Unlike the Mbwelesu or Benbow craters, this crater was particularly shallow and the lava lake was less than 150 meters below us. It was super hot and extremely vigorous.

Like the other craters, Niri Mebluseu’s lava lake drained quickly and underwent catastrophic subsidence and partial crater collapse post 2018. I witnessed a number of landslides when I was there. It was a place you wouldn’t want to hang around for too long. Like Benbow and Marum’s Mebluseu crater, Niri Mebluseu has had post 2018 eruptive activity, forming a new cone and producing lava flows. I haven’t been able to drone it yet, but it’s clearly visible on the satellite imagery.

And lastly, I come to the final crater, Niri Mebluseu Taten, which is a collapse pit to the south of the Niri Mebluseu. Niri Mebluseu Taten was known as “smokey” to the local as it always produced large S02 gas and water vapour clouds but seldom erupted. It was known to have a small lava pond at times. I only once got clear drone footage of it. During the events of 2018, the Taten crater more than doubled in size, particularly to the south. 

Satellite image from 2017. Yellow outline signifies the post 2018 crater.

Today, Taten is perhaps the most stunning of all the craters. It’s gone through the usual greenification around it’s surface, but the crater is now filled with a rainbow of colours. It’s rather quite stunning.

So what does the future hold for Ambrym’s volcano and as so many of you have asked me, when will the lava lakes return?

Well Volcanoes are unpredictable, but there is some very insightful research being undertaken within the scientific community. One particular study notes that the current magma supply rate is comparable to that of what is was before the 2018 eruption and is high enough to promote magma migration towards the surface. What I will say is that the chances of Ambrym erupting again within the next few years is high. It’s not the first time that the lava lakes have disappeared and if history tells us anything, we’ll hopefully see the famed lava lakes once again.

UPDATE: Shortly after finishing the writeup, Ambrym erupted again on January 13, 2024 at 10:17pm local time. The eruption is confined to the Benbow Crater only.


Add comment: