The Life of Volcanic Rocks During and After an Eruption

Volcanoes are constantly growing and changing. Every time a volcanic eruption occurs, new rock is added to the surrounding area. These eruptions play a big part in the formation and destruction of rocks as well as in shaping the Earth’s surface. Yet, we do not know everything about the histories of the volcanoes that previously existed on Earth. Volcanologists—scientists that study volcanoes—can study the types of rocks that volcanoes produce, to gain a better understanding of volcanoes. These rocks vary based on the characteristics of the volcano from which they came. Volcanic rocks are unique because we can study them to accurately discover when and how they were formed. In this article, we explain the processes that make volcanic rocks and formations look different from each other. We also discuss ways that volcanologists can determine how ancient volcanoes were made, by studying the rocks produced during past eruptions.


VOLCANOES AND IGNEOUS ROCKS
While geologists are scientists who study all kinds of rock, volcanologists are geologists who focus on past and present volcanoes, lava, and magma. Volcanologists also study the rocks that LAVA Molten rock that has erupted at the Earth's surface.

MAGMA
Molten rock below or within the Earth's crust.
volcanoes make, looking for clues to help them figure out how and when the volcanoes were formed. By figuring out the conditions that created volcanic rocks, volcanologists can learn about the history of a volcano and possibly predict whether a volcano will erupt again-and what will happen to the landscape and the people living nearby if it does. The rocks surrounding volcanoes give us important data to calculate the volcano's age and to help us answer questions about how the Earth was formed, including when volcanoes erupted and how explosive the eruptions were [ ].
The types of rocks that volcanologists spend their time studying are called igneous rocks. Igneous rocks form when molten rock cools and hardens into solid rock. Molten rock is called magma when it is stored in a chamber beneath a volcano, but it is referred to as lava when it reaches the surface. Volcanoes are created whenever there is a break in the Earth's crust that opens a pathway for magma and gas to escape. Every time a volcano erupts, it changes in shape and size because the lava it releases cools and hardens around it. With time, this can make the volcano higher and wider. The largest volcano in the solar system is called Tamu  large di erences in how volcanoes erupt a ect the type of lava flows they produce.

LAVA FLOWS
Lava flows in di erent ways. Understanding flow types can help volcanologists categorize igneous rocks because features of the rocks change as they cool and harden. Even though lava acts like a liquid, kids.frontiersin.org August | Volume | Article | it is constantly cooling as it moves. This makes it behave di erently depending on its composition and how quickly it is moving. The type of lava flow depends on the lava's viscosity, or resistance to flow. Blocky flows can reach more than meters in height, like a wave growing outward as it travels, before they topple over. Pillow lava (Figure d) only occurs underwater. As the hot lava flows into the cold water, the edge of the flow quickly cools to form volcanic glass, but the inside of the flow continues to move and break through the glassy edge, forming a pillow shape.
Sometimes when lava flows on land, the outside layer of the flow cools and hardens first while the inside layer continues to flow, insulated by the outer rock layer. The result is the formation of a lava tube ( Figure  ). Lava tubes usually only form when the lava is low viscosity and fast moving. As the lava supply to the tube runs out, the tube empties and the hardened outside tunnel remains, leaving behind a long cave stretching from the base of the volcano, with smooth, flat floors like a hallway where the last of the lava flow hardened [ ].
Studying lava flows is interesting because it allows volcanologists to see how a landscape can be formed or dramatically changed because kids.frontiersin.org August | Volume | Article |

CRYSTALLIZATION OF LAVA
Before magma leaves a volcano, it exists in one of three major forms, based on their chemical composition, viscosity, and temperature. They are all extremely hot and too dangerous to measure up close, so they are measured with thermal cameras instead [ ]! The di erent types of magma determine what the cooled, solidified rock will look like. Some magma is very fluid and forms pahoehoe or a'a lava flows, which travel long distances. Other magma is more viscous and cooler, forming blocky lava flows. Magma can also be highly viscous, relatively cool, and form lava domes or blocky lava flows.

LAVA DOMES
A circular mound that results from the slow eruption of viscous lava that piles up around the vents of some volcanoes.
The type of magma, how long it takes to cool, and the gas present during a volcanic eruption impact what an igneous rock looks like after cooling and solidifying. Solidification of molten rock is called crystallization. Igneous rocks that cool underground cool more CRYSTALLIZATION A process where molten (liquid or semi-liquid) rock hardens into solid rock. slowly, giving mineral crystals time to grow within the rock. In these rocks, the di erent minerals are large and easy to see with the naked eye. Igneous rocks that crystallize at the earth's surface tend to cool much more quickly and have much smaller crystals. A volcanic rock made entirely of glass, called obsidian, forms from lava that cools with little to no crystals at all. If lava is flung into the air during an eruption, or if it comes in contact with water, the edges of the lava will also cool to form a glass.
When volcanoes violently erupt, many gas bubbles form in the lava, so it crystallizes into rocks filled with holes where the gas used to be. Rocks with holes formed from gas trapped in the lava are called vesicular rocks. Gases can sometimes be trapped kids.frontiersin.org August | Volume | Article | in the rocks, allowing volcanologists and geologists studying old vesicular rocks to determine which gases were present in ancient volcanoes [ ]. Lava that contains very little gas tends to have no gas bubbles.

TYPES OF IGNEOUS ROCKS
Volcanologists have names for all the various kinds of rocks that are formed from volcanic eruptions. These rocks are first classified into categories, including felsic, mafic, and intermediate, based on the types of minerals they contain (Figure ). Basalt is the most common type of igneous rock made from lava. Basalt is a dark-colored rock in the mafic category, with very little crystal formation. In contrast, andesite, an intermediate rock, is much lighter in color and has many crystals visible without a magnifying glass. Granite is a type of non-volcanic igneous rock, formed from magma cooling slowly underground. Granite is often used for kitchen or bathroom countertops and can be found in a variety of colors, all sharing similar crystal size and mineral compositions.
Rocks without obvious crystals also vary a lot in color and texture. Pumice is an example of a light-colored, felsic, vesicular rock that can float in water. Scoria is also vesicular but is dark, mafic, and denser, unable to float in water. Obsidian, composed of volcanic glass, is a felsic rock that cooled with no crystals. Although obsidian appears to be dark, like basalt, it is felsic in composition. Its dark appearance is due to impurities like iron or magnesium present within the rock.  . End-Triassic mass extinction started by intrusive CAMP activity. Nat. Commun. : . doi: . /ncomms SUBMITTED: June ; ACCEPTED: June ; PUBLISHED ONLINE: August . . doi: . /frym. .

CONFLICT OF INTEREST:
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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ALEJANDRO, AGE:
Hi, my name is Alejandro. I am years old and I live in Ecuador. I like rock music, sports, and animals. I also like trekking. My hobbies are play soccer, do exercise, read, and listen music. I like science because you can discover new things.

CHRISTINA BRENNAN
Christina Brennan is an undergraduate student at Carleton University in Ottawa, Ontario, Canada majoring in interdisciplinary science. She is especially interested in pursuing a career in science communication, and using the skills developed in her undergrad to bridge the gap between disciplines. Since she was years old, kids.frontiersin.org August | Volume | Article | Christina has been designing floor plans of houses on graph paper and continues to do so today through D modeling. Aside from her academic goals, she hopes to day design and build her own net zero home.

VISHNU PRITHIV BHATHE
Vishnu Prithiv Bhathe recently graduated from Carleton University in Ottawa, Ontario, Canada with a Bachelor of Science degree. Ever since he was a child, he has been curious about science and how people use the lessons from science to better the world. He is also interested in entrepreneurship and aims to use scientific research to fuel innovation. In his free time, he likes to ride bikes, paint, read books, and exploring new things.

STEPHANIE ELLIS
Stephanie is an undergraduate student in her final year of the Interdisciplinary Science and Practice program in Ottawa, Ontario, Canada. She is passionate about community engagement and figuring out how di erent systems work, from the human brain to computers. She was inspired by her teachers to continue searching for answers and to follow her passions at a young age.

EMILY MOYNES
Emily is a fifth-year undergraduate student studying Environmental Science at Carleton University in Ottawa, Ontario, Canada. During her schooling, she completed an internship under the supervision of Dr. Steven Cooke on various fish-related projects, resulting in a publication in Transactions of the American Fisheries Society. She is currently completing her honors thesis with Dr. Thomas Sherratt on insect body toughness. She loves acquiring new knowledge and experiences in her field and hopes to day obtain a job exploring animal behavior or working toward conservation-related initiatives.

BRIAN COUSENS
Brian grew up in Montreal where he stumbled across the fantastic world of earth sciences at college and McGill University in Montreal, Quebec, Canada. His interest in volcanoes grew from studies of seafloor volcanism while at UBC in Vancouver and then ocean island volcanoes at UC Santa Barbara. Brian is a Professor in the Department of Earth Sciences at Carleton University in Ottawa, Ontario, Canada, specializing in the geochemistry of igneous rocks. He teaches field courses in volcanic regions such as eastern California, Nevada, Hawaii and Iceland.

SEAN J. LANDSMAN
Sean is a teaching professor in the Interdisciplinary Science and Practice program at Carleton University in Ottawa, Ontario, Canada on the unceded territory of the Algonquin First Nation. He is a trained fisheries ecologist and studies how fish move about their environments as well as how people a ect them. He is also a passionate science communicator and enjoys sharing his knowledge with anyone that will listen! In fact, it was this love of communicating fisheries science that led him to photography and specifically underwater photography. Sean loves to spend time outdoors, especially fishing and hiking, and enjoys tinkering in his basement making things out of wood. *sean.landsman@carleton.ca