Yellowstone National Park was established on March 1, 1872, as the world’s first national park. For over 100 years it was the largest national park in the United States, being surpassed in 1980 by several created that year in Alaska. A rectangle carved out of the state of Wyoming, measuring 54 miles east-west and 63 miles north-south, at 2.2 million acres Yellowstone is larger than the states of Rhode Island and Delaware, combined.

The park was designated a UNESCO World Heritage Site in 1978. Yellowstone is world renown for Old Faithful, one of about 500 active geysers in the park. In fact, more than half the world’s active geysers can be found in Yellowstone NP!

These geysers – and the 1,000 to 3,000 earthquakes felt here annually – are remnants of a volcanic super-eruption that took place here 640,000 years ago and the caldera it left behind, outlined on the map below (more on that later). Part of that caldera has since filled with water, forming Yellowstone Lake, the largest high-elevation lake in North America (most of the park is at an elevation above 7,500 feet). We are camped at Bridge Bay Campground along the shore of the northern reaches of the lake.

The road to Old Faithful from Bridge Bay Campground follows the shoreline west, turning inland at West Thumb, a hydrothermal area like that surrounding Old Faithful, created by a more recent eruption 174,000 years ago – a caldera inside a caldera. From the parking lot at West Thumb there’s a boardwalk through the geyser basin to the lake.

We headed down to the shore…

… and made our way around….

… stopping to note the boiling water emanating from small semi-submerged hot springs in the lake.

The railroad arrived in Yellowstone in 1883, bringing adventurous tourists to the park, many of whom stayed at the Lake Hotel (built 1891), located near Bridge Bay Campground.

The Park was managed by the U.S. Army from 1886 until the National Park Service, created in 1916, took over the management from the Army in 1918. The loop road that connects the 5 entrances to the park was built in 1905 and automobiles were first able to access the park in 1915.

Supposedly, these early visitors to the park would fish along the shore here and then cook their catch in these hot springs.

Leaving the shore and heading back up to the parking lot, the boardwalk passes two large hot springs, Black Pool (below) and the Abyss. The temperature of the water in these springs varies between 100° and 200° F, as evidenced by the steam rising on this relatively warm day.

As I mentioned, above, the heart of Yellowstone NP is a huge caldera formed by an ancient volcanic super-eruption 640,000 years ago. Actually, that eruption was only the most recent resulting from the super-volcano located here; there were two others, one 1.3 million years ago, and the largest of all 2.1 million years ago – their footprints and the volume of ejected material are illustrated, below.

By now, you might be wondering, just exactly what is a caldera and how does one form? Well, you’re in luck, I found the answer:

Experts say that although the Yellowstone super-volcano is still active, it is unlikely that it will erupt again anytime soon… meaning, not within our lifetime. And if there is an eruption, it will be one of those oozing magma flows like we saw at Volcano NP on the big island of Hawaii a couple years ago, easily out-runnable.

But, given how well the “experts” have been doing predicting things these days, I’m not counting on it.