Morning Glory Pool is a hot spring located in the Upper Geyser Basin of Yellowstone National Park, approximately one mile (1.6 kilometres) north of Old Faithful. Measuring about 23 feet (7 metres) in diameter and over 20 feet (6 metres) deep, it is named for its resemblance to the morning glory flower, with a central blue colour surrounded by rings of green, yellow, and orange. The pool’s striking appearance is the result of thermophilic microorganisms, or microbial mats, which thrive in specific temperature ranges and produce pigments that reflect different wavelengths of light.
The intense blue at the centre is due to the depth and clarity of the hot water, which absorbs longer wavelengths of light and reflects shorter blue wavelengths. Closer to the edges, where the water is cooler, various species of heat-tolerant bacteria and archaea create green, yellow, and orange hues. These colours can shift subtly with changes in temperature, flow, and microbial composition throughout the year.
Over the past century, Morning Glory Pool has been impacted by human activity. Visitors throwing coins, rocks, and other debris into the spring have partially blocked its thermal vents, reducing water temperature and altering its microbial community. This has led to increased growth of orange and yellow bacteria, changing the pool’s original deep-blue appearance. The National Park Service has periodically removed debris in an effort to restore some of the pool’s original conditions, though changes in colour have persisted.
Access to Morning Glory Pool is via the paved and boardwalk trails of the Upper Geyser Basin, making it an easy walk from Old Faithful. The route passes numerous geysers and hot springs, providing opportunities to observe a variety of geothermal features. Visitors are required to stay on designated walkways to prevent injury and protect the delicate hydrothermal environment.
Geologically, Morning Glory Pool is part of Yellowstone’s vast hydrothermal system, which is fueled by heat from the underlying magma chamber. The pool’s water originates from precipitation that seeps underground, is heated geothermally, and rises back to the surface through fractures in the rock. Morning Glory Pool remains a notable example of the park’s combination of geothermal activity, vivid natural colouration, and environmental sensitivity.
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