Mount Rainier

Mount Rainier is a massive active stratovolcano located in the Cascade Range.

It sits within Mount Rainier National Park in the Pacific Northwest of the United States. The peak is south-southeast of Seattle and southeast of Tacoma. At 14,410 feet, it is the highest mountain in Washington state. It is also the most topographically prominent mountain in the contiguous United States.

This prominence means it rises significantly higher than the land surrounding it. It is the tallest peak in the Cascade Volcanic Arc.

A stratovolcano is a type of volcano built by layers of lava and debris. Mount Rainier is made mostly of andesite, which is a specific type of volcanic rock. The volcano is highly eroded by wind, water, and ice. Its early volcanic deposits are estimated to be over 840,000 years old. These early layers are part of the Lily Formation. The present-day cone is much younger, at more than 500,000 years old. The mountain's shape has changed many times due to eruptions and collapses.

The mountain's structure includes several distinct summits and features. The highest point is called the Columbia Crest. A second high summit is Point Success, located at the southern edge of the summit plateau. The third named summit is Liberty Cap, which sits at the northwestern edge.

To the east, Little Tahoma Peak stands as an eroded remnant of an earlier, much higher mountain. This peak has a prominence of 1,350 feet. The summit area also contains two large volcanic craters. The larger east crater overlaps the smaller west crater. Geothermal heat from the volcano keeps the crater rims free of ice.

This heat has created the world's largest volcanic glacier cave network.

Mount Rainier is the most heavily glaciated peak in the lower 48 states. It contains 26 major glaciers and many permanent snowfields. These glaciers feed several important river systems. The Carbon, Cowlitz, Nisqually, Puyallup, and North Mowich Rivers all begin at glaciers on the mountain.

The White River is also fed by the Winthrop, Emmons, and Fryingpan Glaciers. These water sources are vital to the geography of the surrounding region.

Indigenous peoples have lived near the mountain for many millennia. They have many different names for the peak in their various languages. A 2025 linguistic analysis identified 20 different names used by Indigenous groups. For example, Lushootseed speakers use names like "sky wiper" or "one who touches the sky." Other names refer to it as a "snow-covered mountain."

The name "Tacoma" is an anglicized version of an Indigenous name. George Vancouver named the mountain "Rainier" to honor his friend, Rear Admiral Peter Rainier. In 1890, the United States Board on Geographic Names made Rainier the official name.

Mount Rainier is considered one of the most dangerous volcanoes in the world. It is included on the Decade Volcano list. This list identifies 16 volcanoes with a high likelihood of causing loss of life. The mountain has a high probability of an eruption in the near future.

Because of the massive amount of glacial ice, eruptions can produce lahars. A lahar is a massive volcanic mudflow. These flows could threaten the Puyallup River valley and other nearby valleys. According to a 2008 USGS report, about 80,000 people live in lahar-hazard zones.

Many communities sit directly on top of older lahar deposits.

Geological history shows that the mountain has undergone massive changes. About 5,000 years ago, a large part of the volcano slid away. This debris avalanche helped create the massive Osceola Mudflow. This event brought the mountain's height down to about 13,000 feet.

More recently, the Electron Mudflow occurred about 530 to 550 years ago. Today, scientists use seismic monitors to watch for activity. An eruption could send ash as far as San Francisco or Vancouver. This makes the volcano a critical subject for geological study in the Pacific Ring of Fire.