Yellowstone National Park, Wyoming

the caldera edges of the super-volcano is outlined in a thick
shadowy edge

Spending time and exploring the caldera of a once Supervolcano seems like a strange choice for a place to visit. However, Yellowstone National Park is  fascinating, eerie, and other-worldly compared to the other parks we have visited. 
We were here for a short stay back in 2002 and were able to get a quick look at the main features.  On this visit we had more time to explore several new areas and learn a lot more about the geology and wildlife of this 2.2 million acre park, the world's first national park established in 1872. 
The park contains the headwaters of the Yellowstone River from which it takes its name. French trappers named the river Roche Jaune which is likely a translation of the Hidatsa Indian name Mi tsi a-da-zi, meaning "Yellow Rock River."

Yellowstone now sits over a volcanic hotspot that has erupted many times through the North American tectonic plate as the plate moved westbound over it.  Over the past 16 million years the hotspot broke through several parts of southern Idaho as that area moved over it.  The hotspot last erupted as a Supervolcano about 640,000 years ago under the Yellowstone area in northwest Wyoming. The center of what is now the park collapsed, forming a 30-by-45-mile caldera or basin. The heat powering those eruptions still fuels the world's largest group of geothermal features: geysers, fumaroles, hot springs, and mudpots. There are more than 10,000 geothermal features in Yellowstone, more than half of the world's total features.

Yellowstone Lake is the largest high elevation lake in North America (7,000 feet elevation), its shore line spanning 141 miles. Another pyroclastic explosion about 174,000 years ago created the West Thumb basin, a smaller circular caldera extending Yellowstone Lake on the west side. So in effect we were exploring a volcano within a supervolcano! In fact, Yellowstone Park lies across four calderas.

West Thumb geyser basin along Yellowstone Lake

The west side of the park is where the most-visited geothermal features are located. It's the region that steams, vents, and bubbles, often smells of rotten eggs, and creates fascinating landscapes. About 1,000 to 3,000 earthquakes occur each year far below the earth's surface in Yellowstone, a lot of them under Yellowstone Lake. These create various cracks in the earth's surface through which steam and heat escape, resulting in the four types of geothermal features found in the park. 

We went on several ranger-led walks in various parts of the park in which the rangers explained the science behind the features we were viewing.  One explained that the hydrothermal features of the park are habitats for organisms called thermophiles that can thrive in extreme heat, and in very acid or alkaline environments.  Their colors range from yellow to orange to brown, and therefore the color of the run-off from geysers gives an indication of the temperature at each location.  The water in some pools is at or near boiling point (199F at this elevation), which is too hot for any organism to survive, and these pools reflect light in a blue color.  The ranger explained that although the blue pools look as inviting as a Caribbean bay, they are too hot to touch, and therefore blue means ''not for you."

a belching, fuming landscape, pockmarked with eerie formations

one of the hotsprings, where water is around 199F degrees

as the park ranger warned, here "blue means 'not for you'" (too hot!)

mud volcano

fumaroles along one of the routes, adding to the other-wordly effect

Old Faithful putting on a great show this morning

Great Fountain Geyser along  Firehole Lake Drive putting on a show just
as we arrived. Eruptions are unpredictable and we were lucky with our timing.

White Dome geyser also along Firehole Lake Drive

Excelsior Geyser discharges over 4,000 gallons of 199F degree water into the
Firehole River

Grand Prismatic Spring, the largest in North America, known for its vivid
colors created by microbial mats surrounding the outer layer of the spring

Sapphire Pool

In Mammoth the ranger explained the different geology creating the travertine terraces.  He explained that much of the central area of the US was once under an ocean, and the surface formed as sedimentary layers of limestone.  When the hotspot erupted under Yellowstone, it created a caldera that eventually filled with magma, forming hard rhyolitic and basaltic rocks.  The Mammoth area is located outside of the caldera, and therefore the underlying rock is sedimentary limestone.  They believe earthquakes created a fissure from the caldera hotspot to the Mammoth area, and hot gasses and water are forced along this fissure and escape through vents in the Mammoth area.  The hot water dissolves carbon dioxide from the gasses and creates an acidic solution that dissolves limestone on its way up.  On the surface the limestone precipitates out of the solution as travertine, forming the beautiful white terraces.  This is a much faster process than the silica-based deposits from geysers over rhyolite, and so changes in the Mammoth travertine terraces can be observed in a matter of a few years.

The Canyon Area, in the eastern section of Yellowstone Park, features the colorful Grand Canyon of the Yellowstone River, the Upper Falls(109 feet) and Lower Falls (308 feet). The Yellowstone River flows for 20 miles through the canyon which is approximately 24 miles long, between 800 and 1,200 feet deep, and from one to three quarters of a mile wide. 

Lower Falls

Tower Falls (Upper Falls)

Yellowstone River 

A ranger-led hike along the canyon rim provided us with pretty vistas of the canyon, river, and the colored canyon walls.

With a 45 MPH speed limit in the park, it took a long time to drive to the sights. We spent three full days exploring the various features and went on several ranger-led walks. Learning about the geology of the park, its formation and the constantly changing geothermal features was fascinating. It felt like I was getting an up-close view into the underworld. 

It was again surprising how many visitors were in the park at this time of year, most of them from Europe and Asia. The tour buses and rented campers were present throughout the park, creating heavy traffic which often came to a standstill particularly when herds of bison decided to cross the road. 

We saw a lot of wildlife while at Yellowstone. Bison were a regular sighting. 
In fact, the day we pulled into Bridge Bay  Campground, I saw a bison casually strolling into the campground. Later we noticed that he was lying down between camp sites. 

One morning on our way to Mammoth Hot Springs, we had to stop and wait while an entire herd of bison crossed to the other side of the road. They took their fine time. At the Mammoth Hot Springs store, I was amused by a sign that said:Stuck in bison jam. Register closed. We had just experienced a jam of our own that very morning.

Returning from Mammoth later that afternoon, the same herd was still gathered at the lake they had crossed to.

On our way to one of the visitor centers, we saw a bison swimming across the river. That event generated all sorts of excitement as cars and campers pulled over to watch and photograph.

bison in the river

On another morning on our way to the Geyser Basin, we crossed paths with a herd of elk who were also crossing the road. In the early morning light it was difficult to spot the cows and a couple of young ones and as we slowed down, a stag with his magnificent rack emerged from the forest to join the cows. More cows ventured out of the forest and yet another stag followed, stood in the middle of the road, eyed us suspiciously, then began to bugle. A third stag with an even larger rack emerged. And he too began to bugle to his cows who followed. It was both exciting but also scary because elk are quite unpredictable at this mating time of year and are known to charge at anything, including cars. And here we were right in the middle of it all.

We also saw trumpeter swans along our drives from Canyon Village to Tower-Roosevelt. They were easy to spot along the river, their white color a vivid contrast to the khaki surroundings.

Tomorrow we move on again. Our next stop, about 420 miles east, is Devils Tower National Monument. We plan to take a couple of days to get there, stopping in Sheridan overnight.