Yellowstone National Park has a deep and rich geological history.  The location of the park lies over a hot spot – a hole in the Earth’s crust – where magma liquid can rise up to the surface.  The particular location of Yellowstone and nature of this hot spot have created what we have come to know as a supervolcano.  The first, and largest, eruption of the Yellowstone supervolcano was 2.1 million years ago, followed by one 1.3 millions years ago, and finally the most recent supereruption, 640 000 years ago.  To give you an idea of the magnitude of the blasts, you can see the large squares below.  The first and largest of the blasts produced 2500 cubic kilometres of ash.  In the picture below, each one of those little cubes is the equivalent to the ash from the eruption of Mt. St. Helens.  So Yellowstone is no joke.  Remnants of the eruptions can be found as far south as Nevada or far north as Yukon territory.

Underneath the surface of Yellowstone is a complicated plumbing system, filled with water that is heated by the magma chamber beneath (about 5 miles down or so).  This produces a hydrothermal system responsible for the 4 geothermal features we can see on the surface: Hot Springs, Fumaroles, Geysers and Mudpots (shown in the diagram below – left to right).    There are over 10 000 geothermal features to see in the park.  Because of the scalding hot water below the surface there are signs reminding you not to touch, and many elevated boardwalks to keep tourists off the fragile ground.

On day 2 in Yellowstone we saw all 4 of these features while working our way around the south Yellowstone loop.

Hot Springs:  Hot Springs are caused when water is heated by the supervolcano and circulates freely to the surface.  Minerals and thermophiles (more about those here), along with refracted light create the beautiful colours that we see in these geysers.  The springs and pools formed are the most common hydrothermal features in the park.

West Thumb Geyser Basin – Connected to Yellowstone Lake, home of gems such as the Black Pool (the green and orange one with white salt around the edge), Abyss Pool (shiny green pool) and Fishing Cone.  West Thumb is a caldera within a caldera.

Midway Geyser Basin – Home to the famous Grand Prismatic Spring (the orange and steamy one) and Excelsior Geyser (the blue one).

Biscuit Basin – Crossing the Firehole River to see the Sapphire Pool (bright blue and super deep) and many other pools of bright colours and rivers of orange and yellow.

Upper Geyser Basin – home of the Morning Glory Pool, one of the most colourful hot springs in the park.  Ray and Meg walked a 4.4 km trail to see this gem (start at Old Faithful).  The colours are spectacular.

Norris Geyser Basin – Made up of 2 parts, the Back Basin and the Porcelain Basin (seen in the pictures below).  The Back Basin is where you locate the Steamboat Geyser.  Though Steamboat is the tallest geyser in the park, it is also completely unpredictable, which is why I focused my attention to the hot springs on the Porcelain side.  The bacterial mats of green and orange were so unreal.  Also seen was the Pinwheel Geyser, Crackling Lake and Black Growler Steam Vent.

Mudpots: Mud pots form when acidic water dissolves rock into mud and clay.  Hydrogen sulphide gas then bubbles and produces a wonderful rotten-egg smell, along with bubbling mud.  Thickness of the mud varies in colour depending on mineral (and silica) content, and with precipitation, allowing it to range from a diluted thin watery soup to a more concentrated thick pancake batter-like substance.

Artists Paint Pots – a short hike up over small pools and bacterial mats brings you to a view of the orange and mud coloured terrain – which looks like it has been painted – and at top, pools of thick bubbling mud.  Because of it’s current thickness, it was more of a “plopping” mud, than a rolling boil.

Mud Volcano – A second basin is home to the Mud Volcano, Mud Geyser, Mud Cauldron, Dragon’s Mouth Geyser and Sulphur Cauldron.  The Mud Cauldron and Volcano you can see show bubbling mud – much thinner than those we saw at the Artists Paint Pots.  Dragon’s Mouth Spring is the creepiest sounding spring, trapped in a cave.  We tried to imitate it’s sound, but we couldn’t do it justice.  The Sulphur Cauldron has a pH of 1.2 – which makes it one of the most acidic features in the park.  We didn’t get to see the Mud Geyser as a family of bison decided to take over the trail we needed to walk there, and the rangers refused to let us walk through them.  Probably a smart move on their part.

Geysers: Geysers are like hot springs, but there are constrictions in their plumbing, which causes pressure to build up, and eventually leads an eruption.  2/3 of the worlds geysers are found in Yellowstone. There are over 300 geysers in the park.

Old Faithful – The most famous feature in the park is a geyser – and it also happens to be the most predictable.  Old Faithful erupts every 70 +/- 10 minutes.  We ended up needing to wait for about 20 minutes to see her blow.  There are signs all over the area with her next eruption time.  She even has her own twitter handle.

Fumaroles: Also known as steam vents, these are like geysers, but with so little water that it turns into steam before it reaches the surface and in turn produces a very loud hissing noise.  These are the hottest features in the park

Fountain Paint Pots – Home to a wonderful mudpot, which is much redder than the white (silica rich) pots found further north.  The mudpots here are also much thinner mud, so they look like a very angry boil. The video and picture below is of Red Spouter – Which depending on the time of year has both a mudpot and a fumarole. In the video it is easy to see the boiling mud close to you, and right behind is the steam and LOUD LOUD noise of the fumarole.  This is not static or poor video.  It is really that loud.  You can barely hear your neighbour talking.

In 9 hours we managed to log 15+ km of strolling along boardwalks and short hiking trails.  Some of these features shown are close to the parking lot, and other required 1-4 km to get in to see them.  Most of them involve walking on boardwalks to avoid breaking the surface and falling into unexpected boiling water just beneath.  The land and waters are both hot and acidic – even more so when you get into the various basins.  Most of these features are found in the south end of the park, where are the high mountains, trees, rivers and canyons are found slightly more to the north, when they are no longer inside the caldera of the supervolcano.  It is possible to spend a weeks walking all the trails to see many more of the features.  I have to admit I’ve only ever seen the ones that are easy to access – that’s what happens when you try to hit everything you can in on day.  Also the reason while we will keep going back.  But great places are always worth revisiting.  The sounds, smells, sights and feel of head radiating off the earth’s surface all make Yellowstone an experience for the senses.  My best advice – go slow.  Savour it.  Put the camera away from time to time and just look out on the horizon to the foreign landscape and let it blow your mind.  Thinking back it still seems surreal, and I can’t imagine ever getting sick of it.