What is volcanic ash?

Volcanic ash is often talked about on the news when a volcano erupts or threatens to blow itself up but what actually is it?

It might surprise you to know that the term ‘ash’ (when we’re talking about volcanoes) is actually used to describe the grain-size of material ejected by a volcano. ‘Ash’ refers to all volcanic material of <2mm.

Pyroclastic grain-size classification
Grain-size classification for volcanic material (Cas & Wright 1988)

Therefore ash can be made up of a range of different materials all less than 2mm, including: rock fragments, crystals and fresh volcanic glass (AKA pyroclasts)

Components of volcanic ash
Volcanic ash can contain rock fragments, crystals and fresh volcanic glass (called pyroclasts)

Find out more: The wonders of volcanic ash – an introduction

How do volcanoes make diamonds?

Before you say yes to that proposal, where DID your diamond come from?

Diamonds are hot stuff – they have been an important status symbol for hundreds of years, and form under extremes of heat and pressure, here’s how:

Diamonds are often found in Kimberlite or Lamproite pipes, these are sub-vertical rocks that formed when magma from deep within the Earth forced its way into shallower levels of the Earth and solidified. This magma (molten rock) may have originated from >100 miles (>160 km) deep, within the mantle. At this depth the rocks can experience very high pressures and temperatures that allow carbon to crystallise as diamonds as the magma rises towards the surface and cools.

If these deep magmas squeezed their way up to the surface of the Earth and erupted then diamonds may have been incorporated into volcanoes. However, our diamonds generally formed 1 – 3 billion years ago, so any evidence of volcanoes has long gone. We now collect all of our diamonds from Kimberlite and Lamporite pipes – areas where the solidified diamond-bearing magma is now exposed.

Fun fact:

  • The worlds oldest diamond is 4.3 billion years old, the width of a couple of human hairs (70 micrometers),  and was found in the Jack Hills of Australia in 2007


The importance of understanding sediments

Sedimentary rocks are an understated source of information when trying to understand present and past eruptive activity at a volcano. They therefore form a very important focus of much volcano research. Here I will explain some of the reasons why studying and understanding sediments is so important in volcanological research.

Sediments and volcanic material in Iceland
Sediments vs. volcanic deposits in Iceland. Credit: S.Wanmer 2017

Why are sediments important? – the rock cycle

Sediments are an important component of the rock cycle. The rock cycle in general includes sediments which come from the weathering and erosion of pre-existing igneous and metamorphic rocks, in turn these sediments may be compressed and transformed into metamorphic minerals by heat and pressure. They can also be melted and become a component of magma and subsequent igneous rocks. In turn these metamorphic and igneous rocks can become exposed on the surface of the earth and worn away by weather, landslides (gravity), water and ice and end up as sediments.

This is all well and good, but, what about material that isn’t weathered from pre-existing rocks? What about all the volcanic material thrown out during eruptions and deposited across the land and throughout the sea?

In most cases this material, the finest grains in particular, end up within the sedimentary environment. These are environments in which eroded grains of pre-existing rocks are dominant (not to mention all the substances and bits and pieces that come from biological sources!), for example in rivers, the sand on the beach, as well as, the silt and mud in estuaries and the sea. This leaves us with a bit of a dilemma…

Igneous vs. sediment

In general, any rock or pieces of rock produced from magma and intruded below the surface, or erupted onto the surface of the earth are considered to be types of igneous rock. Igneous rocks however can take two forms: intrusive (those that remain below the ground) and extrusive or volcanic (those erupted above ground). Volcanic material is what we will consider here.

When volcanic material (AKA tephra) is deposited onto the ground it is a ‘primary’ volcanic deposit. The material has been erupted and sits where it first touches the ground. However, in most environments this material will be re-mobilised, for example, by wind, water or gravity.

As soon as these grains move, they are technically no longer ‘primary’ volcanic material and no longer form a ‘primary’ volcanic deposit. Technically these re-mobilised grains are now effectively sediment – they will behave like any other sedimentary grains of the same morphology, being influenced by different conditions in the surrounding environment.

Therefore, there is plenty of debate about when volcanic grains become a sediment, and how the deposits that they form should be named. Commonly deposits composed of volcanic grains that are not ‘primary’ are termed volcaniclastic sedimentary deposits.

There are still some complications with this, for example:

  • How far does a volcanic grain have to travel before it comes a volcaniclastic sedimentary grain – 1mm? If such a small distance as this is considered for renaming of the grain from ‘primary volcanic’ to ‘volcaniclastic’ then shouldn’t all volcanic deposits be re-named as volcaniclastic sediments?
  • How would you be able to tell if a volcanic grain has travelled 1mm or 1km from the place where it was originally deposited? – this is the centre of some important and often very confusing research (including my PhD)!
  • And, I’m sure many more complications – feel free to comment with your own thoughts on this.
Wind blown material at ancient submarine volcano
Wind blown sediment or volcanic material at the base of an ancient submarine volcano, Iceland. Credit: S.Wanmer 2017

Understanding sediments is just as important as understanding the volcanic grains present within a volcanic or sedimentary rock sequence.

Layers of volcanic material can often be found within layers of sedimentary material. A full understand of all of these deposits will help piece together the history of the volcanic grains. For example, you might be able to work out the environment in which the volcanic material was deposited (e.g. water and if this was the water of a river, lake or the ocean), as well as aiding identification of ‘primary’ volcanic and volcaniclastic sedimentary deposits. In turn, this can help you when trying to understand the eruptive history of a volcano, including the type of eruption and eruption dynamics. Finally, this can then aid in identifying the hazards posed by different types of eruption at an active or dormant volcano, potentially preventing the loss of life during the next eruptive episode.

Disney’s Moana – Lava vs. Water

Disney’s recent release ‘Moana’ is not only a great family film but is also a superb film for its geology. Throughout the film geological formations create stunning backdrops, which are pretty accurate in terms of their geological nature. Not only does the film contain some wonderfully animated geological back-drops but also the tale of a lava monster which cannot enter the sea. In terms of real life volcanology how accurate are the tales and imaginings in this film? In this post I’m going to give some insights into the reality of lava vs water and the geological phenomenons shown in Disney’s latest animation.

An island of ancient lava

The island landscape of the film has as similar appearance to that of the Polynesian, or Hawaiian islands within the Pacific Ocean, with sharp jagged mountain peaks and glistening blue waters. At the beginning of the film the geology of Moana’s home island is alluded to with the presence of black lava on the beach. This lava appears to be thin and has an intricately folded ropy surface – this is thin pahoehoe lava. The thin nature of the lava could suggest that this was the leading edge of a lava flow which then froze when its supply of lava, or the source eruption, ended. It may also be possible that larger, thicker amounts of lava are present beneath the white sandy beaches that surround it on this imaginary shore.

Following many years of tradition on the island, the chief places a flat hexagonal rock onto a pile when they begin their ruling. These hexagonal disks of rock are typically found around areas of columnar jointed lavas which have been weathered on the surface of the earth for many years (even many hundreds or thousands of years). The original columns form as a thick lava cools and contracts (columns can also form in dykes and sills). The presence of these special rocks in the film suggests the presence of ancient igneous activity on the island.

Giants causeway
Columnar jointed lava forming hexagonal columns and plates, Giants Causeway, Northern Ireland. Credit: Mayer 2003

Later in the film thick units of these columnar jointed rocks are accurately depicted as huge towering columns like those seen at Devils Tower National Monument in the USA. There has been a lot of debate regarding how the large columns of the Devils Tower formed, with some suggesting that aliens are responsible for these formations! However, columnar jointing like this can be found all over the world, from Scotland to Hawaii, and it is a natural phenomenon that can be explained by the natural contraction of a lava or magma during cooling. Some mysteries still can’t be fully explained, like how such great thicknesses of molten rock can form perfect columns that are several hundreds of meters in length.

Devils Tower National Monument
Devils Tower National Monument made from columnar jointed igneous rocks, USA. Credit: Faulkingham 2003

Lava vs. water

A major part of the film involves a terrifying lava witch which sits in the sea on a small lava covered reef. When Moana comes face to face with this monster she can be heard saying that the ‘lava can’t enter the water’. But, how does this compare to real life?

Hawaii is a prime example of a currently active volcano where lava is actively found flowing into the sea. Most of the time this produces little danger as the lava happily flows off the land and into the sea where it cools into lava rocks, with a hiss and some steam. In the film when the lava witch touches the water the lava of her skin steams and rapidly cools forming a shell of solid lava. This really does happen in the real world. When lava cools rapidly (known as quenching) the outer part of the lava solidifies, it may produce steam and some smaller fragments of rock at the same time. The lava beneath this outer layer may still be molten and will be somewhat insulated by the surrounding skin of cooled rock. The lava witch can be seen explosively expelling the hardened outer shell of skin, after touching the water, to reveal more molten rock inside.

lava and surtseyan eruptions
Lava entering the sea (left) and a typical hydrovoclanic eruption from Surtsey with white steam clouds and black cock’s tails (right). Credit: US Navy, Street 2007 & NOAA

The lava witch is surrounded by the sea and only lies on a relatively thin reef of lava, it is therefore likely that if this was a real eruption then it would be a hydrovolcanic eruption. This would involve large amounts of water coming into contact with magma erupting from a vent. In the film the lava witch is surrounded by black billowing clouds of ash, in reality (for a hydrovolcanic eruption) this is more likely to contain larger amounts of white steam and less black ash than is portrayed. This is because large amounts of water are likely to be involved in the eruption, more so than the amount of ash produced. An exception to this would be if the erupting vent was completely isolated from coming into contact with sea water in which case only a highly explosive eruption would be likely to produce the large billowing clouds of black ash in this way. During hydrovolcanic eruptions the eruption clouds produced often contain episodic black (ash rich) ‘cock’s tails’ rather than continuous billowing black clouds full of ash.

Would a lava monster in the form of a lava flow exist in this situation in reality? The interaction between the lava and water in a hydrovolcanic eruption is typically highly explosive with no actual lava flows produced, unless, the vent was isolated and interactions with sea water had ceased. Therefore the lava witch probably would not exist in this setting until the vent was been sealed off from the sea and the lava was protected and able to flow from the vent.


To wrap up this post delving into the reality of the animated geology of Disney’s film ‘Moana’ it can be said that the geology is very well portrayed. And you can actually learn a few things about volcanology even from an imaginary lava witch!

Floating rocks

There are only 2 rocks that can float on water, and one of them has a fiery origin. Pumice. A light rock full of vesicles (bubbles) that has the ability to spread joy to anyone who has ever encountered large blocks of it in the wild.

Not even volcanologists can resist the ‘strong-man’ photo opportunity when large blocks of pumice are around!

Pumice contains at least 50% vesicles, or voids that formed from a large amount of bubbles within the original magma. When the erupted magma cools these bubbles remain in the rock as vesicles.

Many of the vesicles will be joined to other vesicles and form an interlocking maze of tubes throughout the rock; however, others will remain completely isolated and it is these that give the pumice it’s prolonged bouyancy in water.

Pumice from unobserved eruptions in our oceans can be found many hundreds to thousands of kilometres away from their source, and may be the only evidence of some eruptions in the ocean.

Eventually a floating pumice will become water-logged and sink to the depths of the ocean, becoming preserved within the rock record for millions of years.

The only other rock to float on water is called diatomite – a rock formed from the skeletal remains of billions of microscopic organisms called diatoms.

9. Standing on the shoulders of giants

It is not the mountain we conquer but ourselves. – Sir Edmund Hillary

As you stand at the summit of a volcano, gazing down on the world around you, you experience a huge lump of emotions. The immense pride that you managed to fight against your internal voice for the last 4+ hours, the one that’s been telling you that ‘this was a stupid idea, I can’t do this…’ or, ‘I should just quit and go home to a nice cup of tea’. Relief, that you did it, you finally made it to the top. Immense satisfaction and awe, when you look at how incredible the view is, and how amazing the world can be; how you can’t believe that you almost turned around 2 hours ago. And also, sometimes, immense dread, because you know that you’ll have to go back down again! In this blog post I will share my experiences of standing on the shoulders of some incredible sleeping giants.

Mount Merapi 2014 summit sunrise
Sunrise from the summit of Mount Merapi, Indonesia. Credit: SWanmer 2014

The night before

After mentally preparing myself for the challenges of climbing a volcano I knew that it’s really important to get lots of rest the night before. However, the excitement and nerves that flow throughout your being are most defiantly not going to let that happen. The night before my first climb of a volcano I didn’t sleep at all, which went against everything that I had mentally prepared for. I was ridiculously excited.

The morning

Waking up early to start a climb certainly isn’t an issue when you’ve been awake with excitement all night. When the alarm went off I almost lept from my bed and felt like I could run all the way up the volcano straight away. Like an eager child waiting for their parent to wake up on Christmas morning, I was ready and rearing to go.

Permits are required to reach the summit of Mount St. Helens, USA.

The climb

As I started the climb my excitement reached a peak, a peak that was impossible to maintain for much more than half an hour. Gradually the excitement turned into an internal battle to keep going and not give up. It’s a tough physical and mental challenge to keep going up a 45+ degree slope for several hours on end. Even with the summit in sight and a clear view of the route ahead  it’s a real struggle. Most of the time the summit lies in view for several hours, so that not even the sight of the summit motivates you after a while. Not only are there the physical aches that come with walking in this terrain for extended periods of time but there are also the constant mental checks that you make each time you step forward. The ground around you may be jagged or loose, and unforgiving if you fall, and you have to constantly calculate where you will put your feet next.

Standing on top of the world

There is nothing that can prepare you for all the emotions and relief that you feel when you finally heave your tired body up onto the summit rim of a volcano. No matter how I describe this I won’t be able to do the experience any justice.

As you reach the summit of a volcano absolutely every feeling washes over you. It is a feeling that I will never ever forget, almost like a shock to your system, the feelings remain vivid for years to come.

When I reached the summit of Mount St Helens. This was something that I had always dreamed of, yet I never expected the views that surrounded me. Looking out across the world, with the biggest smile on my face, and a tear in my eye. Relief and awe striking me down as I took in the whole experience, wishing that I could stay there forever.

Hugging Mount St Helens
Hugging the volcano: at the summit of Mount St Helens in 2012

However, reaching the summit of Mount Merapi, was a completely different experience. The climb had been the most difficult thing that I had ever done, starting at 1am and lasting the rest of the dark night, it was filled with excitement and panic attacks. As I stood at the summit watching the sun rise over Indonesia, I was struck by an immense feeling of dread. It was absolutely amazing to have reached the summit after a 5-6 hour climb but I knew that we would then have to hike the same route back down, and I was absolutely terrified!

Standing on the shoulders of the magnificent beast that is Mount Merapi, Indonesia, in 2014

Making memories

Everyone has a different summit experience, but I promise you that it will be one of the most incredible things that you will ever do. It will challenge you physically and emotionally and test you to your limits. But will give you the added satisfaction that you’re standing on top of a wild and untamed beast, one that could destroy itself within your lifetime, giving you the chance to experience something that might not exist several years or decades down the line.


Hazards to consider before visiting a volcano

What are the volcanic hazards that all adventurers should consider before starting to explore a volcano?

Active volcanoes can present a unique set of hazards for adventurers and researchers alike; it’s important to consider all the risks before visiting a volcano:

  1. Rapidly changing weather conditions and visibility (-do you need to take a jumper or a rain jacket, or even a torch?)
  2. Shifting volcanic gases – always be aware of what the volcano is doing before and while you are exploring, poisonous volcanic gases can rapidly change and become life threatening
  3. Rough, loose and slippery terrain, with cracks and crevasses – keep an eye on your surroundings at all times
  4. Eruptions – be aware of the current activity levels of the volcano and if any alerts or restrictions have been put in place; phreatic/steam explosions can happen at any time without warning
  5. Rock falls – should you wear a hardhat, or are there any areas that you should avoid?

Let someone else know what your plans are and your route so that if you and your friends/group get into trouble you will always have someone looking out for you.

Find out more about fieldwork and adventure safety and equipment in the Adventure Blog

8. Fieldwork and Adventure Safety

When visiting or working in any outdoor environment it is important to prepare yourself and take some simple precautions to help you to stay safe and happy. In this blog post I will list some of the simple precautions that you should take when embarking on any volcanic adventure.

1: Plan your route and tell a friend

Before you go anywhere you will need a plan of where it is that you are going and what you will be doing. Some simple things to consider are:

  • What is the activity level of the volcano? Have any warnings or restrictions been issued?
  • How will you get to and from your desired destination? When is the last bus/train etc?
  • How far will you have to walk?
  • What will the terrain, weather and/or tides be like?
  • Will you have phone signal?
  • Will you have a map, and are you able to use it?
  • Are there any specific hazards that you might face during your journey and how will you deal with these?
  • What action would you take in an emergency? Is there a mountain rescue team, for example, and how would you contact the emergency services?

During fieldwork all of these things are usually considered and planned for by conducting a risk/hazard assessment.

Specific hazards that you might need to consider for volcanic environments include:

  • Rapidly changing weather conditions and visibility
  • Shifting volcanic gases
  • Rough, loose and slippery terrain, with cracks and crevasses
  • Eruptions (phreatic/steam explosions can happen at any time without warning; some volcanoes give little or no warning before erupting)
  • Rock falls

It’s usually safest to travel in a group but sometimes you may be with one other person or completely on your own. In any case it’s good to let someone else know what your plan is and contact them if you get into trouble e.g. you get lost. A good plan to put in place is to let that person know what time you will be back from your adventure, and make a plan to put into action if you do not contact them at/before that time to let them know that you are safe.

This is good practice for adventures anywhere in the world, not just in volcanic regions!

2: Do you have the right equipment? 

For any trip it’s important to consider the weather conditions and the terrain. For volcanoes it can often be beneficial to have sturdy walking boots with good ankle support. Here are some other suggestions:

  • The temperature on a volcano can change rapidly so make sure you have some extra layers of clothing so that if it gets cold (or there is an emergency) you can stay nice and warm (gloves and a warm hat are always handy to have even in the middle of summer!).
  • Waterproofs are an essential for many volcanic adventures. A waterproof jacket can act as wind protection as well as protection from rain or damp, moisture rich clouds. A pair of water proof trousers can add to this protective layering.
  • Whether you’re on your own or part of a group it’s important to carry some basic first aid equipment. If you’re on your own then you might be the only one around to help yourself if you get in trouble, but importantly you will have the equipment for anyone else to help you, or so that you can assist others.
How prepared are you for an emergency? Credit: FEMA 2006, Wikimedia Commons

3: What’s in your first aid kit?

Basic first aid kits contain gloves, bandages, slings, swabs, scissors, safety pins. They often also contain a small booklet on what to do in certain emergency or medical situations. Here are some other suggestions for your first aid kit:

  • A whistle – encase you need to attract attention in an emergency.
  • Re-hydration packsencase of dehydration – particularly in hotter, drier or warmer, more humid environments.
  • You can also carry an emergency blanket which is usually a small packet containing a big foil bag, or a thick, brightly coloured plastic bag, specifically designed for outdoor emergencies. This can be used if you are stranded or the weather changes rapidly, or it can be used in a medical situation to warm someone, provide wind and rain protection and attract attention.

The best level of protection may be attendance on a course for first aid training that is tailored to the kinds of situations that may arise during outdoor adventures such as fieldwork or hiking/trekking etc.

4: Other useful things to carry

Additional tools that can be extremely useful to pack, for example, a torch, and emergency food e.g. Kendall Mint Cake. Emergency food supplies are those that you will NOT consume during your adventure but are a back-up encase you find yourself in a tricky situation. Extra layers and extra water to what you already have can also be useful but these do also take up space and add weight to what you will already have to carry.

Sometimes it might be useful to carry/wear a hardhat to protect you from falling debris. Volcanic material is often very loose and crumbly and small rockfalls can happen frequently without warning. A hardhat can also be beneficial at active volcanoes where the volcano is unpredictable…even if it seems quiet it should be remembered that phreatic explosions (caused by water coming into contact with hot rock) can blast volcanic material out of the crater at any time without warning).

A final remark

It’s important to remember that volcanoes can be dangerous and unforgiving places, but with the right level of preparation you can give yourself the best chances of having a safe and happy time. All in all though volcanic terrains can be fascinating and enchanting places to explore for pleasure and for work!


7. Staring into Hell

The first time you stare into the belly of an active volcano is a moment that you never forget. In May 2016 I was given the opportunity to join some dear friends in Nicaragua, an amazing country with a large density of active volcanoes. As part of our adventures we took a trip up to the summit of Volcan Masaya where we peered down into ‘the gates of hell’.

Our journey began with a tour guide service in the city of Granada where we booked on to a night-time crater tour. Our trip included transport, guide, entry into the volcano park and gas masks just in case the volcano was emitting too many gases. In the end we got all of these things except for a guide, but the whole experience was no less mind-blowing.

We were driven from Granada to the city of Masaya where we joined a long queue which stretched a long way down the dual carriage way. We slowly slowly crept forward and eventually made it to the park entrance where a fee was paid and we were able to continue in our long queue through the park up to a manned road block. It was dark and humid, all around was vegetation and impatient people getting in and out of their cars. Through the trees a starry night sky could be seen, interrupted every now and again by bright flashes of lightning from a distant storm.

We learnt that only a certain number of cars are allowed up to the summit at a time and when it’s your turn you are given a maximum of 15 minutes to park the car, get out, and peer over the edge into the crater below.

It was finally our turn….We slowly drove in convoy with the other qualifying sightseers up towards the summit. We cleared the trees as we entered into a lava field surrounding the volcano. As we approached the summit the clouds above the vent turned a deep red. The silhouette of crucifix appeared on the horizon against the deep red sky with the occasional flashes of lightning from a nearby thunderhead, the air smelling more and more sulfurous as we got closer. It was incredible…

When the car stopped at the summit we jumped out and raced towards the barriers on the craters rim….the sight that met us was unbelievable. Boiling, shifting, bubbling, glowing orange lava with puzzle pieces caused by various regions of cooled lava floating on the molten mass. The hubub of the sightseers around us was pretty loud but if you cupped your ears in the direction of the lava lake you could hear the frothing and rushing of the bursting, mixing lava below.

You get sucked into a trance by the amazing sights and sounds of the boiling lava and its difficult to pull your self away. Soon though our allotted 15 minutes was over and everyone at the crater was herded back into their cars and told to make their way back down.

There was so much to take in at the craters rim, it wasn’t until afterwards when looking through the images and videos that I had taken that the experience truly sank in. This was an experience that I will never forget. If you happen to be visiting Nicaragua I highly recommend going up to peer into the gates of hell at the summit of Volcan Masaya. Not only for the incredible experience but also because this is one of only a handful of active lava lakes in the world! It’s therefore a very unique experience and I promise that it will be something that you never ever forget.

What IS a supervolcano?

Supervolcanoes may be hot in the media but what are they really?


The word ‘supervolcano’ often appears in the media with threats of a global humanitarian crisis and the end of modern civilisation, but first thing’s first: what IS a supervolcano?

A supervolcano is defined as being a volcano that has experienced a large eruption that produced 1,000 km3 of rock (known as the Dense Rock Equivalent or DRE).

Comparison of the volumes of material erupted by different eruptions, those that produced more than 1,000 km3 were ‘super-eruptions’ Credit: USGS

By erupting such a large volume of material the volcano will commonly then collapse in on itself and create a caldera. This is why these eruptions are sometimes called ‘caldera-forming eruptions’ within the volcanological community.

A caldera is bound by faults and is not like a normal volcanic crater which is produced when material is blasted outwards from a vent or there is smaller-scale subsidence.

Some of the best examples of calderas include, 1. Crater Lake, USA. 2. Mount Somma, in which Vesuvius has subsequently grown, Italy. 3. Krakatau, Toba and Tambora in Indonesia. 4. Lake Taupo, New Zealand. 5. Las Cañadas, a series of at least 3 overlapping calderas in which Teide has subsequently grown, Tenerife. However, many of these calderas were produced by very large eruptions, but did not necessarily produce 1,000 km3 of material to classify them as super-eruptions.

Crater Lake, Mount Mazama
Crater Lake, a caldera formed by the eruption of Mount Mazama, USA. Credit: S.Wanmer 2015