Ocean 'on fire' twice in three days

Last week, the ocean caught fire. Twice. That’s not something you can say everyday. Firstly, the Gulf of Mexico hosted a glowing ‘eye of fire’ not far from an offshore oil rig; then, just two days later and on the opposite side of the world, a massive fireball erupted from the Caspian Sea, creating a column of fire that could easily be seen from 45 miles away. Sally Le Page spoke to geologist Mark Tingay from the University of Adelaide to find out what actually happened…

Mark - There was a leak in a gas pipeline near one of the major oil and gas fields in the Gulf of Mexico. That causes a lot of gas, obviously, to leak out of the pipeline, and lightning ignited that bubbling gas and caused the big eye of flame that we all saw on social media.

Sally - It did look incredibly dramatic. It didn't even look real to be perfectly honest with you.

Mark - It was incredible. And yeah, it is something that unfortunately we do see occur whenever we have a major fire associated with a major hydrocarbon leak in oil and gas fields.

Sally - How can an ocean catch fire? It's surrounded by water, water puts out fire, doesn't it?

Mark - Yeah, that's what you'd think isn't it? The water should put out a fire. In reality, it's not the water that's on fire, it is just the gas. So all the bubbles of gas, all the methane, natural gas, that's coming out of the ground, bubbles up through the water. And then once it gets to the surface, it's essentially feeding that fire. But the water itself actually isn't on fire. It just looks like it.

Sally - The images from that were, for me, it seemed like a kind of once in a lifetime sort of image, but then it happened again! We had a second fire in the oceans, this time in the Caspian Sea. What happened there was it the same deal?

Mark - The fire in the Gulf of Mexico was a broken gas pipeline near an oil platform. The fire in the Caspian Sea was actually a perfectly natural event where we had a big fireball that jetted out from the eruption of a major mud volcano on a very small island in the Caspian sea.

Sally - Wow. I've never even heard of a mud volcano before. What is a mud volcano?

Mark - So a mud volcano is a part of the Earth where subsurface water and mud essentially come out of the ground. So if you think about a volcano, a normal volcano, those erupt molten rock and ash. A mud volcano is a bit like that, but it erupts watery mud. And along with it, it can also erupt a lot of gas.

Sally - How big are they? Do they look like the mountains that we think of when we think of a volcano?

Mark - Most of them in the world are very small things that might only be tens of metres in size. The ones in Azerbaijan are quite unusual in that they do look like real volcanoes. They can be hundreds of meters tall.

Sally - So you've got this liquid mud, you've got these bubbles of natural gas erupting. What then sets that off to create what was such a dramatic mushroom cloud going into the sky of fire?

Mark - We're not a hundred percent sure because of course it's not something that we can easily test, but there's two main ideas. One is that it's just a very sharp drop in pressure. There's been a lot of simulation that suggests that just the very sharp drop in pressure could be enough to ignite the gas on its own. But I think another possibly quite likely situation is that when you've got all this very violent eruption of mud, it's not just water and clay. It's got boulders inside; rocks, cobbles, big chunks that can be half the size of a car. And these are things that are being violently thrown into the air. And of course they can bang together and potentially cause a spark. And you really just need one spark to ignite that huge amount of gas.

Sally - So this is the natural equivalent of striking two flints together.

Mark - That's right. Yes.

Sally - What are the environmental consequences of these fires happening in these oceans?

Mark - It's a good question, and I'm not exactly sure what the consequences are going to be of, for example, the Pemex fire. If it's mostly gas, then most of the gas would have burnt. And so your biggest issue there is of course, the emissions and its contribution to climate change. The real concern would have been how much gas might've been dissolved in the seawater. And if there was any oil that also was released, which of course we know from oil spills can cause huge devastation over a large area. Pemex has denied that there was any environmental damage or major oil spill. From mud volcanoes, of course, it's a natural phenomenon. They do happen quite regularly in that part of the world. They do erupt quite a lot of oil. They can erupt quite a lot of gas. I haven't heard of any oil spills visible from the mud eruption in the Caspian. The impact on the environment there is probably quite minimal, and of course it's a natural event. But mud volcanoes do contribute significantly to Earth's natural methane budget, that of course we take into account when we're looking at the impact on the climate cycle.