Midway Geyser Basin: the incredible colours of Grand Prismatic Spring

The name Midway Geyser Basin may not ring a bell, but surely you know one of the hot springs in it: Grand Prismatic Spring! Midway Geyser Basin is therefore one of the main attractions of Yellowstone, not to be missed!

Located between Lower Geyser Basin and Upper Geyser Basin, Midway Geyser Basin, which bears its name, offers an impressive group of hot pools and ancient geysers.

To access it, a large carpark with sanitary facilities is located in the immediate vicinity of the road. But with the popularity of this place, expect a parking lot that is often full during peak months. From the car park, wooden pontoons lead to the various phenomena, the total distance to be covered is 1 km.

We noted an influx almost tripled between September 2013 and October 2017. As park visitation is increasing, popular areas such as this one are becoming increasingly popular.

We start by crossing the Firehole River, which flows peacefully along the road below the active zone. Although hot water runoff from the upstream hot basins flows into the river, it keeps the temperature rather warm, even cool (between 30°C and 5°C depending on the location).

1Excelsior Geyser

Once past the river, the pontoon splits in two to form a long loop. Leaving on the left, we discover the impressive Excelsior Geyser which was once a real monster! He was active until 1980, spitting water up to 91 meters high! His eruptions were spectacular! That same year, its chimney unfortunately collapsed on itself, forming the hole visible today. Since then, the geyser only erupted once in 1985, with a 9 meters jet.

Today Excelsior Geyser has become a warm water swimming pool whose light blue color indicates that its temperature reaches 90°C. Even so, it continues to discharge between 15,000L and 17,000L of boiling water per minute into the Firehole River.

2Grand Prismatic Spring

Admire the pool from the ground

The pontoons then take us to the famous Grand Prismatic Spring. If I tell you this is the third largest hot spring in the world! With its 112 meters wide, Grand Prismatic is incredibly large and known throughout the world for its rainbow colours, which reveal themselves by taking a little altitude.

From the ground, it is unfortunately difficult to take all the measure and beauty of Grand Prismatic Spring, but it is interesting to observe the ochre gradients that spread on its sides, when the water temperature is lower.

Depending on the temperature of the air, steam will be released more or less from the hot pool. In summer, you will notice the slight gradient of colours visible from the ground, as well as the blue in the centre of the pool. When it is cooler, water vapour makes it difficult to observe colours, unless the wind is blowing.

As with all other hot springs in the park, it is the presence of bacteria that form a colored mat around the source. Colours depend on several parameters, including water temperature. The warmer this one is, the more the colors will turn greener, while the warmer temperatures will produce yellow, ochre and reddish, even brown colors. It is therefore easy to guess that the hottest temperatures are at the centre of the spring. On the other hand, the blue color indicates a water close to the boiling point, therefore very hot and not conducive to the development of bacteria. Blue shades are produced by the depth of the water and not by the presence of bacteria that live at lower temperatures, and therefore in the periphery.

Admire the spring from the overlook

To better observe the colours of Grand Prismatic Spring, it is therefore necessary to take a little altitude. For this purpose, a viewpoint has recently been built on the heights to the southwest of the basin. Its access is from the Fountain Flat Drive, a wide gravel bike path that also serves the Fairy Falls Trail, a small hike that I recommend you continue to the end if you have some time in front of you.

To get there, take the road south and fork to the Fairy Falls Trail car park. The small car park has recently been enlarged to accommodate the many vehicles that now park there since the opening of the belvedere. From the car park, you will have to walk for 1.2 km before reaching the point of view. Only the last 250 meters climb to reach the promontory.

From here, a wooden lookout offers a beautiful view of Grand Prismatic Spring. A warm weather will allow more revealing the colors of the hot spring.

Expect to have people at the lookout, even after a short walk to get there.

In 2013 the lookout was not yet official, nor furnished, so we climbed on the other side to observe better the fabulous colors of the great hot spring. Today, this access is forbidden, but this small ascent through the fir trees was one of our most beautiful memories at the time.

3Turquoise and Opal pools

Let's go back to the Midway Basin, from the pontoons near the Grand Prismatic. Continuing the visit, we discover Turquoise Pool and Opal Pool, two small hot pools (be careful because the names of the two pools are often inverted on the maps).

The first, Turquoise Pool, is a simple hot spring with dark blue waters. As for Opal Pool, it is at first sight a nice hot spring with ochre and orange edges. It is actually a geyser, in spite of its name and calm, hot spring-like appearance. Rather active in the 1980s, it produced an eruption of up to 9 meters high once a day, but the basin dried up in 2005, before returning to water in 2008. Since its eruptions have become rare.

Following the pontoons, we now arrive at the junction of the loop, which will complete the turn of Midway Geyser Basin. The return is then done by the same way up to the parking lot.