Summer in Illinois can feel unbearably hot, but how hot is that exactly?  At 80ºF, Illinoisans can be found enjoying the sunshine and the reprieve from our winters.  At 100ºF, Chicagoans complain incessantly as cautionary heat warnings show up on billboards.  But what about, 200ºF?  Or 1000ºF?  These are the real extreme temperatures, and they are so hot that they literally melt rocks.  Believe it or not, parts of our very own planet heat up to these temperatures. 

To find temperatures like these, temperatures that can melt rocks, you would have to look below the surface of our planet.  If you could reach a thermometer with a camera all the way into the center of a volcano, you would be able to observe rocks melting all around you.  In fact, it would be so hot that your thermometer would likely melt.  And your camera, too.

liquid rocks

The crater of Kawah Ijen in Java, Indonesia. Photo by Dana Simmons 2018.

So what is a volcano exactly?

A volcano is a place where the Earth’s crust has split, allowing liquefied rocks from below the crust (in the mantle) either leak or explode out onto the surface.  They form as the result of tectonic plates pulling apart or thinning, or from plumes in volcanic hotspots. Although all volcanoes work this way, this is where the similarities end.  Some volcanoes are underwater in trenches, some are under glaciers, and others appear as enormous mountains.  Although they come in many varieties, they can all be classified by shape, lava texture, or activity status.

liquid rocks

The Earth’s Layers, EdPlace

Vulcán de Pacaya: Liquid Rocks in Costa Rica

The typical volcano that most people learn about in school is consists of a giant mountain with red lava exploding out the top.  Fortunately, it is relatively rare to see an eruptions that brings up enough lava to form an entire mountain.  For example, the Vulcán de Pacaya in Guatemala was fairly dormant for 70 years before it began to erupt again in the 1960s.

Now, it erupts nearly every year.  Most of its eruptions are minor events, and on many days, a continuous stream of fiery, liquid rock flows steadily down the mountain, delighting adventurous hikers. Hikers on the Vulcán de Pacaya will find cords of hardening lava, composed mainly of basalt and aluminum, cooling along the trails.  After stumbling through piles of ash on the way to the top, hikers who reach the summit will be treated to wondrous views of melted rock flowing down the mountain.

liquid rocks

Vulcán de Pacaya Lava Flow, Guatemala. Photo by Dana Simmons 2009.

Ring of Fire

The Vulcán de Pacaya is just one of the many active volcanoes in Guatemala.  Why does Guatemala, such a small country have so many volcanoes?

Guatemala falls along what is known as the “Ring of Fire.”  The Ring of Fire describes a path encircling the Pacific Ocean that hosts 452 volcanoes across parts of Indonesia, Japan, Russia, Alaska, California, Central America, and South America.  The Ring of Fire came about because of shifting tectonic plates.  As the plates shift, the land splits, leading to volcanic eruptions of varying intensity.

Most of the largest eruptions in the past 11,000 years have taken place along the Ring of Fire (Oppenheimer 2011, Eruptions that Shook the World).  Some are so severe that they are classified as “Vesuvian” eruptions, meaning that they devastate nearby towns, often covering them completely in volcanic ash and blocking the sun.  From July to December of 2017, the Vulcán de Fuego in Guatemala erupted and exploded every few hours with 12 major eruptive episodes and killed over 100 people and covered the surrounding communities under enormous piles of ash.  (You can get involved with ongoing relief efforts here and here.)

Kawah Ijen

On the other side of the Pacific, Indonesia boasts an ever-changing collection of hundreds of islands formed by volcanoes.  Indonesia is home to 76 volcanoes – more than any other country in the world.  As they erupt over time, new islands form and the land area of the country grows.  Such a volatile landscape poses many serious hazards for permanent residents.

One of Indonesia’s largest islands, Java, contains unique volcano called Kawah Ijen, which doesn’t spew typical red lava, but instead spews sulfur.  Make no mistake though, all the sulfur coming out of Kawah Ijen is completely melted into liquid, just like any other volcano.  But unlike other volcanos, as you approach Kawah Ijen, you start to smell the stinky scent of sulfur and thoughts of rotten eggs come to mind.  The smell intensifies as you climb the mountain, and just before your nostrils begin to wish they could close up shop, you reach a station where you can rent gas masks.

Besides the stench, the gas masks protect you from breathing in the hydrogen sulfide gas (H2S) gas in the air, which is toxic.  As you climb over the ridge at the summit and down he rocky trail into the crater (the opening of the volcano), you see clouds of yellowish gas rising from the depths of the volcaco. As the gas clouds flow by, they sting your eyes.  These aren’t rain clouds – these clouds are composed of liquid sulfur.  When there’s a break in the clouds though, you’ll be treated to a fascinating view of liquid sulfur dripping out of the surrounding rock.  The liquid sulfur is orange, and it turns yellow as it hardens.

liquid rocks

Liquid Sulfur Inside the Crater of Mt. Ijen. Photo by Dana Simmons 2018.

In other cracks in Java’s Kawah Ijen volcano, it is so hot that the sulfur ignites into bright blue flames.

liquid rocks

Sulfur ignites and produces blue flames on Kawah Ijen. Photo by Olivier Grunewald for National Geographic.

Life on such a landscape is no walk in the park.  In the camp around Kawah Ijen, there’s no running water or power lines.  To make money, miners from Java trek down into the crater of Kawah Ijen twice per day to collect baskets of sulfur.  Wearing rubber-soled boots to avoid slipping, they carry out loads of sulfur that weigh about 150 lbs each on their backs.  Though slipping is certainly a concern, the major heath risk facing these minors is the poisonous sulfur gas.  While tourists rent gas masks, the miners usually just tie a bandana around their head to cover their mouth and nose.  The long-term health effects of this practice are dire, but the miners continue their work because it’s relatively high-paying, and they need to feed their families.  Learn more about Kawah Ijen in BBC’s episode of Human Planet:

Land Recovery after an Eruption
liquid rocks

Plants return amid volcanic ash on the Arenal Volcano in Costa Rica. Photo by Dana Simmons 2014.

Not all volcanoes are explosive threats to everything around them.  At least, not once they’ve been dormant for a while.

Some volcanoes, such as the Vulcán Arenal in Costa Rica have been “resting” for so long (since 1968) that plants are beginning to reclaim the areas that were covered by lava.  In the process of reclaiming land, insects and seeds come back first, and they settle around the edges of the hardened lava and charred earth.  Over decades, the insects and bacteria break down pieces of lava and turn them back into soil.  When there is sufficient soil, seeds will grow into plants, and animals who eat those plants will return.  Gradually, larger plants will grow, and larger animals will rebuild their habitats among those plants and trees.

Recovery is an exceedingly slow process, and if interrupted by another eruption, it starts all over from the beginning.

Underwater Volcanoes

When we think of a volcano, we mostly refer to mountains with lava coming out, above the ground.  However, most of the Earth’s volcanic activity takes place deep in oceanic trenches – also along the Ring of Fire.  In fact, five of the Earth’s largest volcanoes are underwater — they’re the volcanoes that formed the Hawaiian Islands.

Around 70% of the Earth’s surface is covered by water, so it makes sense that most of the world’s volcanoes are underwater.  One special type of volcano that can be found underwater is a hydrothermal vent, which produces bubbles of very hot gas that rise to the surface of the ocean.  Only special organisms that can withstand extreme heat (called thermophiles) can live around these vents, and it’s believed that these vents are where life began.  When there is enough activity and an occasional blast with sufficient lava, sometimes we get a new island!

Remember Disney Pixar’s short film “Lava” (below)?  It’s a great illustration of how underwater volcanoes make islands.

Next time you’re traveling, check out the natural attractions in your destination.  Are there volcanoes to hike?  What stage of eruption or recovery are they in?  Do you see any plants starting to grow back or is there a fresh lava trail?  Are there communities destroyed by eruptions in need of supplies?  Get involved with nature!


  • Dana Simmons

    Dana Simmons is a Co-Editor-in-Chief of Science Unsealed and holds a Ph.D. in neurobiology from the University of Chicago. She is an active participant in the global SciArt community, and her innovative neuron art has been exhibited around the world. Dana is a medical writer for a Chicago agency that serves pharmaceutical and biotechnology companies. SciArt website: Twitter: @dhsimmons1

Cultivated For Your Curious Self

Keep Your Learning Going

Did you enjoy this article? You’re our kind of person. And we think you’ll love these posts from our team of experts.

Total Solar Eclipse on April 8, 2024

Total Solar Eclipse on April 8, 2024

On April 8th, 2024, a total solar eclipse will sweep across North America, from Mexico to the Maine-Canadian border. For those who experienced the spectacular solar eclipse of 2017, this one will be similar, crossing the United States from west to east and passing through or near several major metropolitan areas. And while its path is quite different this time, Carbondale, Illinois, a reasonable destination for Chicago-area residents, will once again be on the line of totality.    

Just a little background on eclipses:  Lunar and solar eclipses are not uncommon – they each occur about twice a year when the moon is crossing the ecliptic, the path of the sun in the sky.

Two women representing the Illinois Science Council at an event.

Don’t Have the Time? Donate Today.

We know you’re busy. but you can still help. We’re an independent 501c3 nonprofit, and all donations go to bringing science to the community.

Donate Today