Earth Rocks!

National parks are magnificent places to witness geology in action, and to learn how to coexist with our dynamic planet. This year, we are celebrating Earth Day and National Park Week by sharing the types of rocks found on public lands as well as national parks that showcase our nation’s geodiversity.

Be sure to join us on social media as we explore the earth sciences and stewardship this week and every week. And, remember that natural objects, such as rocks and minerals, contribute to the beauty and wonderment of our national parks and you should leave these natural objects as you found them.

Igneous Rocks

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Igneous rocks (from the Greek word for "fire") form when hot, molten rock (magma) crystallizes and solidifies. Magma comes from deep within the Earth, near active plate boundaries or hot spots. Magma that rises to the surface is called lava. Hawai'i Volcanoes National Park and Acadia National Park both feature igneous rocks.

Hawai'i Volcanoes National Park

Hawai‘i Volcanoes National Park protects some of the most unique geological, biological, and cultural landscapes in the world. Extending from sea level to 13,677 feet, the park encompasses the summits of two of the world's most active volcanoes: Kīlauea and Mauna Loa.

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Kīlauea is the youngest and most active volcano on the island of Hawaiʻi, and one of the busiest in the world. In recorded history, Kīlauea has only had short periods of rest. It has covered almost 90% of its surface in lava flows within the last 1,000 years.

Mauna Loa is the largest active volcano on the planet. Meaning "long mountain" in Hawaiian. With its broad, rounded slopes, it is the quintessential shield volcano. The volcano makes up roughly 51% of Hawaiʻi Island and stands 13,678 feet (4,170 meters) above sea level. It rises an astonishing 30,000 feet (9,144 m) from the bottom of the sea, a greater height than Mount Everest.

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Molten lava that reaches the surface during volcanic eruptions is still adding mass to the island of Hawaiʻi. In fact, the island itself is made up of flows that have built upon one another over many thousands of years. Molten lava is only visible during an eruption, but its solidified form makes up the island of Hawaiʻi.

Lava and magma are the same substance, but in different places. The term magma refers to molten rock that is still within the Earth. Once it breaks through the Earth's surface, it is called lava.

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According to Native Hawaiian tradition, molten lava is the manifestation of Pele, the volcanic deity and creator of new lands. According to tradition, she is embodied by the lava and natural forces associated with volcanic eruptions.

Acadia National Park

The landscape at Acadia National Park tells the tale of a time when fire and ice covered these lands. The geologic history of Acadia National Park stretches back in time through millions of years to the formation of the oldest rocks on Mount Desert Island and continues through today by the persistent forces of erosion (the process of rocks gradually wearing away).

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The landscape that we know as Acadia had its beginnings more than 500 million years ago, when mud, sand, and volcanic ash were deposited in an early ocean. With time these sediments were buried, and pressure turned them to rock. You can find evidence of this rich geologic past across the park.

The varied landscape of Acadia National Park is the result of continuing geologic processes. The weathering of granite ridges is one such activity. Large joints, or fractures, in the rock form square blocks. The joints enlarge and expand when water fills them and freezes. Eventually the rock breaks away from the cliff, leaving behind granitic rubble and bright pink scars on precipitous rock faces.

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At 1,528 feet in elevation, Cadillac Mountain is the highest point in Acadia National Park. The Cadillac Mountain Granite is among the largest bodies of granite on the island, and it is also one of the oldest in the region (~420 million years old).

Sedimentary Rocks

Sedimentary rocks form from deposits of pre-existing rocks or pieces of once-living organisms that accumulate on the Earth's surface. If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.

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These rocks often have distinctive layering or bedding and create many of the picturesque views of the desert southwest. Badlands National Park and White Sands National Park have examples of sedimentary rocks.

Badlands National Park

Badlands National Park is known for its geology and paleontology. You may have heard the term “badlands” before, but not in reference to this park. That’s because in addition to being a geographic term, describing Badlands National Park in South Dakota, this word is also a geologic term.

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The lowercase version of badlands is used to describe most terrains that look like the formations in our park. They are typically characterized by soft sedimentary rocks that erode easily. The formations in the park are the result of two simple processes: deposition (process of rocks gradually building up) and erosion.

The Badlands formations have a lifespan of approximately one million years. They erode at about one inch per year. Scientists estimate that in the next 500,000 years, the Badlands will have eroded completely.

Badlands buttes contain millions of years of history -- much of which can be unpacked with the sciences of geology and paleontology. There are several types of rocks that can be found in the Badlands, including sandstones, siltstones, mudstones, claystones, limestones, volcanic ash, and shale.

There are badlands formations all over country in places like Wyoming, Utah, North Dakota, Colorado, and Nebraska. You can even check out badlands formations in the National Park Service like Theodore Roosevelt National Park in North Dakota and Petrified Forest National Park in Arizona, or visit one on National Grasslands like Toadstool Geologic Park in Nebraska. There are also badlands formations throughout the world in Canada, New Zealand, Italy, Spain, and Argentina.

White Sands National Park

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White Sands National Park is one of the world's great natural wonders. Great wave-like dunes of gypsum sand engulf 275 square miles of desert, creating the world's largest gypsum dunefield.

The story of the world’s largest gypsum dunefield began 280 million years ago when the Permian Sea covered this area and gypsum settled on the sea floor. The formation of the dunefield continues today in an endless cycle of erosion and renewal.

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White Sands National Park preserves a major portion of this unique dunefield, along with the plants and animals that live here.

Metamorphic Rocks

Metamorphic rocks form when high temperatures and pressure act on a rock to alter its physical and chemical properties. These conditions often stretch, twist, and fold the rock as it cools. 

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In metamorphic rocks some or all of the minerals in the original rock are replaced, atom by atom, to form new minerals. Grand Teton National Park and Shenandoah National Park both feature many examples of metamorphic rocks.

Grand Teton National Park

Grand Teton National Park has a fascinating natural and cultural history. The Tetons are one of the youngest mountain ranges in North America. They have been uplifting for less than 10 million years, making them "adolescent" mountains, as compared to the "middle-aged" Rockies (50-80 million years old) or the "elderly" Appalachians (more than 300 million years old). Over billions of years and natural forces including earthquakes, glaciers, and erosion have shaped this magnificent landscape.

The Teton Range contains some of the oldest rocks in North America, similar to those exposed in other major mountain ranges of the western U.S., including the Bighorns, the Gros Ventre and Wind River ranges.

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A 2.7 billion-year old metamorphic rock called gneiss makes up much of the Teton Range. These rocks were formed when sea floor sediments and volcanic debris were buried up to 18 miles deep as two tectonic plates collided – similar to the collision of India and Asia today forming the Himalayas.

The intense heat and pressure at these great depths changed or metamorphosed the sediments into today's rocks, separating different minerals into lighter and darker layers. Watch for the zebra-striped layers as you step over rocks on your hike!

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The Teton fault is still active and capable of generating a magnitude 7.0-7.5 earthquake. Geoscientists have dated the three most recent earthquakes at about 5,900, 8,000, and 10,000 years ago.

Shenandoah National Park

Shenandoah National Park rises above the Virginia Piedmont to its east and the Shenandoah Valley to its west. The story of Shenandoah’s mountains is the story of two mountain ranges, spanning over one billion years of Earth’s history.

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Current geological activity in Shenandoah National Park is a result of natural and man-made forces acting on the surrounding mountains and valleys. Freezing and thawing can result in rockfalls and spalling from cliff faces. Severe thunderstorms and rain events can cause flooding and associated erosion. In extreme cases, large amounts of rain can cause landslides. Some forces act together to produce geological change.

A wind storm may bring down trees that were killed in a wildland fire on land where, in turn, severe rain could cause significant erosion. Most often these events are relatively small, but over millions of years, these small events produce sizable changes in the land. The result is a landscape undergoing constant change.

Learn More About America’s Geologic Legacy

You can enhance your appreciation of geoheritage sites and scenic vistas by understanding the fundamentals of geology.

Learn how plate tetonics shape our landscapes, why geologists use relative age dating to determine the depth of geologic time, discover geoscience concepts, and more by visiting the America’s Geologic Legacy section of nps.gov. To explore geology concepts, visit the U.S. Geological Survey’s Geology directory.