Crater Lake, a beauty spot located in the southern part of Oregon, is renowned as the deepest lake in the United States and the seventh deepest in the world. The formation of Crater Lake is a captivating tale of violent volcanic eruptions and their aftermath, leading to the creation of a stunning natural wonder.
The Beginning: Formation of Mount Mazama
The foundation of Crater Lake lies in the formation of an ancient volcano known as Mount Mazama, which was part of the Cascade Range volcanic arc. Mount Mazama began to form approximately 400,000 years ago, due to a series of volcanic eruptions that constructed a complex of overlapping shield and stratovolcanoes.
The Cascade Range and Mount Mazama
Mount Mazama is a part of the chain of volcanoes known as the Cascade Range, stretching from Lassen Peak in California to Mount Garibaldi in British Columbia. The Cascade Range is a perfect example of a fundamental concept in geology where the interaction between tectonic plates results in a chain of volcanoes forming parallel to and inland from the plate boundary.
This specific area is known as a subduction zone, a collision zone where the dense Juan de Fuca Plate, an oceanic plate, sinks below the less-dense continental North American Plate. As the Juan de Fuca plate dives deeper beneath the Earth’s crust, temperatures and pressures increase causing the plate to partially melt and release less dense material within the rock (like water, gases, etc.). This less dense material rises, melting and absorbing surrounding rock as it bubbles upwards to form magma. This magma eventually collects and creates magma chambers just below the crust of the Earth. These chambers behave similarly to a soda can, staying dormant most of the time unless a sudden disruption occurs. Just as a sudden and violent shake of a soda can will cause the liquid to explode when opening, volcanoes will react to this quick change in motion and pressure by erupting onto Earth’s surface.
The Growth of Mount Mazama
Mount Mazama grew for almost half a million years. The earliest rocks visible today, which are 420,000 years old, form Mount Scott on the east side of Crater Lake. Over time, lava flowed from many volcanic vents, overlapping and building an irregularly-shaped mountain. By about 8,000 years ago, Mount Mazama may have stood as high as 12,000 feet above sea level.
The Cataclysmic Eruption and Formation of the Caldera
The calm beauty of Crater Lake obscures the violent forces that formed it. In an explosive eruption around 7,700 years ago, known as the caldera-forming event, Mount Mazama erupted violently and collapsed. The eruption, resulting from the magma chamber emptying, forced the walls of the volcano to collapse inward, creating a caldera, a large basin-shaped volcanic depression.
The Eruption and Collapse
The eruption of Mount Mazama was a tremendously powerful event. A column of hot gas and volcanic rock was ejected high into the air. This magma fell to the earth as fragments of frothy white pumice and volcanic ash. Layers of ash from this eruption can still be found in the soil as far away as Alberta, Canada, more than 1,000 miles away.
During the eruption, so much magma was expelled from the inner chamber that the volcano lost its structural integrity. Without any support, the walls collapsed into the empty void to form a caldera measuring roughly five miles from north to south and six miles east to west. This process is known as caldera formation.
The Formation of Crater Lake
After the cataclysmic eruption and collapse of Mount Mazama, a deep caldera was left behind. Over the course of several hundred years following the creation of the caldera, rain and snow filled the basin to a depth of 1,943 feet, creating Crater Lake. This lake is isolated from surrounding streams and rivers and has no inlet or outlet. Its primary input is from annual precipitation in the region. The average annual precipitation is 168 centimeters, while the average snowfall is 13 meters.
The Post-Eruption Landscape
Following the eruption and subsequent collapse, several smaller eruptions continued inside the newly formed caldera. These eruptions created a series of small lava domes on the caldera floor, including the partially subaerial Wizard Island cinder cone, and the completely submerged Merriam Cone.
The Formation of Wizard Island
One of the most recognizable features of Crater Lake is Wizard Island, a volcanic cinder cone that forms an island at the west end of the lake. This island was formed from subsequent eruptions within the caldera after the initial collapse. The peak of the island is roughly 230 meters above the average surface of the lake, and the land area of the island is 128 hectares.
The Formation of Phantom Ship
Another notable feature of Crater Lake is Phantom Ship, a natural rock pillar located near the southeastern shore of the lake. It is a remnant of an ancient volcanic vent that remained after the collapse of Mount Mazama. This rock formation appears as a ghost ship, especially in foggy and low light conditions, adding to the mystical aura of Crater Lake.
The Potential Future of Mount Mazama and Crater Lake
Despite the serene and tranquil appearance of Crater Lake today, it remains part of a restless geological landscape. The long history of volcanism at Mount Mazama strongly suggests that this volcanic center will be active in the future. Although the area has been dormant for about 5,000 years, there is every reason to expect some kind of future volcanic activity in the place where it has been occurring for almost half a million years.
A Look at the Future
Given the violent history of Mount Mazama and the ongoing hydrothermal activity along the lake floor, scientists predict that there will be another eruption someday in the future and Mount Mazama might grow back. However, no volcanic activity has occurred at Mount Mazama in the last 5,000 years; studies of lake sediments show no evidence of magma movement beneath the earth’s surface; and there have been no earthquakes of the kind associated with volcanic activity.