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How Volcanoes Form Glass

laze from a volcano.
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Volcanoes have gotten a reputation as being destructive, especially with the most recent explosion occurring on the Big Island of Hawaii. And rightfully so—lava flows destroy trees, crops, neighborhoods and anything else in their way. But when one thing is destroyed, another is sometimes created. In this case, it’s glass. Yes, glass.


Lava Lessons

Magma is mostly made up of only two elements—silicon and oxygen—which are superheated by the earth’s core to a sweltering 1,250 Celsius. As it cools, it begins to rise to the earth’s surface. At this point, it is referred to as lava. As the magma rises to the surface it causes pressure against the earth’s crust which must be released. Sometimes the lava creates cracks and seeps out of the surface. Other times, massive amounts of pressure cause the picturesque and frightening images of explosions that one sees in volcanoes such as Kilauea on the Big Island in Hawaii. Hot lava flows like a liquid, yet slows down as it cools. Eventually, when the lava cools completely it forms igneous rock.

cooling lava

How Lava Becomes Glass

So if lava forms rock, what does this have to do with glass? Lava can either cool very quickly or very slowly depending on what it comes in contact with. In many cases, a water source is eruptions sites. Lava coming in contact with water will cool it quickly. In this case, the chemical reaction causes the lava to turn into a type of igneous rock that is uncrystallized—just like glass. Glass is actually neither a solid nor a liquid, but has a non-crystalline physical structure somewhere between the two.  This glass created by lava can come in many forms, the most popular being pumice or obsidian. Obsidian is a type of igneous rock that is black and shiny. It is brittle which can cause it to fracture and create sharp edges similar to other glass products.


The Dangers of Lava

When lava cools quickly it is extremely dangerous or even deadly and caution must be taken to avoid areas where this is occurring. The chemical reaction that occurs releases Sulphur dioxide gasses as well as extremely tiny pieces of glass into the air. These minuscule pieces of glass can be damaging to skin, lungs and eyes.

When rapid cooling occurs at a volcanic site, a large plume with a mix of the Sulphur dioxide and glass particles can usually be seen rising into the air. The hazy gas is often referred to as “laze” which was coined by a mix between lava and haze.

laze - lava haze mix

How Volcanoes are Constructive

After this violent and destructive-looking process takes place, the end result can be a good one. Larger cooled portions of lava can actually create new masses of land that did not exist previously. And all of those tiny glass particles? Once they settle, those can help to create beautiful tropical sand beaches. So the next time you take a trip to the beach, consider how glass may have played a part in creating that sand between your toes.

volcanic black sand beach


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Daniel Snow

Daniel Snow serves as the Vice President of Operations for and is also a contributing editor. He earned a Bachelor’s Degree in Business Management from George Mason University and has a background in the real estate industry. After high school, Daniel even worked at a family-owned glass shop for a short period of time and is an Auto Glass Safety Council certified installer. In his free time, Daniel enjoys being outdoors, especially around the water where he can be found surfing, fishing, and boating. He has a passion for bringing old vehicles back to life and loves working with his hands to restore cars, boats, and motorcycles. Find out more about Daniel on Linkedin.

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2 Responses

  1. Ive seen lava glass rocks on the beaches of Lake Ontario. How old would this lave glass rock be?

    I have pictures of it and I can send them to you to look at.

    Thanks for your reply

    1. Hi Oral,
      Thanks for the comment! This is a great question, but unfortunately not our area of expertise. Some of the oldest formations of volcanic glass date back 322 million years ago. In North America, glass could have shifted toward the Lake Ontario region as late as 800 BC, according to our research. For more accurate accounts, it would be best to get with a local archaeologist or geologist. Good luck!

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