The Alaska Range and Denali: Geology and Orogeny (U.S. National Park Service)

NASA Graphic

The force of the Pacific Plate pushing northward creates tension between the two plates. The build-up and sudden release of tension as these plates slip by one another triggers earthquakes.

Much the way the hood of a car buckles under the force of a collision, the process of subduction causes the uplift of the Alaska Range, as well as the coastal ranges. There are two major faults that contribute to the uplift of Denali. They are the Denali Fault and the Hines Creek Fault. Land south of the faults moves to the west relative to the north at a rate of about 1 centimeter per year. A large bend in the Denali Fault directly north of Denali causes rocks to bunch up. Denali happens to be in this bend; this is one of the reasons it is so tall. The forces that caused the uplift of Denali continue today.

Scientists know that Denali rises at a rate of one half of a millimeter per year. That may not seem like much, but at that rate it will rise one kilometer in the next two million years—a brief period in geologic time. Its composition is another reason that Denali has grown to such a great height. It is mainly igneous rock granite. Denali’s granite formed below the Earth’s crust as part of a batholith. A batholith is a bubble or mass of magma within Earth’s crust. Plutons are parts of batholiths, defined by their chemical composition.

The chemical composition of the magma determines the type of rock that will crystallize. Other intrusive igneous rocks (rocks that cool within the crust rather than at the surface) include gabbro, diorite, and pegmatite. Granite usually happens to be less dense than much of the rock that surrounds it. Over millions of years, a granitic pluton will float slowly towards Earth’s surface, as it has in the case of Denali. Denali sort of “popped” up to the surface, much like a cork held under water will pop up when released. Just remember that “popping up” can take millions of years! Erosion of Earth’s surface rocks also helped expose the granitic rocks that make up Denali. Granite is also very resistant to erosion. The forces of erosion, that is water, ice and wind, have a hard time wearing Denali’s rock away. The rock pushes up faster than it is eroded, so Denali continues to grow. Subduction, uplift, and the lack of erosion have all contributed to Denali’s great height.

The force of the Pacific Plate pushing northward creates tension between the two plates. The build-up and sudden release of tension as these plates slip by one another triggers earthquakes.Much the way the hood of a car buckles under the force of a collision, the process of subduction causes the uplift of the Alaska Range, as well as the coastal ranges. There are two major faults that contribute to the uplift of Denali. They are the Denali Fault and the Hines Creek Fault. Land south of the faults moves to the west relative to the north at a rate of about 1 centimeter per year. A large bend in the Denali Fault directly north of Denali causes rocks to bunch up. Denali happens to be in this bend; this is one of the reasons it is so tall. The forces that caused the uplift of Denali continue today.Scientists know that Denali rises at a rate of one half of a millimeter per year. That may not seem like much, but at that rate it will rise one kilometer in the next two million years—a brief period in geologic time. Its composition is another reason that Denali has grown to such a great height. It is mainly igneous rock granite. Denali’s granite formed below the Earth’s crust as part of a batholith. A batholith is a bubble or mass of magma within Earth’s crust. Plutons are parts of batholiths, defined by their chemical composition.The chemical composition of the magma determines the type of rock that will crystallize. Other intrusive igneous rocks (rocks that cool within the crust rather than at the surface) include gabbro, diorite, and pegmatite. Granite usually happens to be less dense than much of the rock that surrounds it. Over millions of years, a granitic pluton will float slowly towards Earth’s surface, as it has in the case of Denali. Denali sort of “popped” up to the surface, much like a cork held under water will pop up when released. Just remember that “popping up” can take millions of years! Erosion of Earth’s surface rocks also helped expose the granitic rocks that make up Denali. Granite is also very resistant to erosion. The forces of erosion, that is water, ice and wind, have a hard time wearing Denali’s rock away. The rock pushes up faster than it is eroded, so Denali continues to grow. Subduction, uplift, and the lack of erosion have all contributed to Denali’s great height.