“Yellowstone National Park is an immense, active volcano - one of the largest and most violent on earth”
But it is very hard to envisage that the Yellowstone National Park is sitting on top of a volcano, as there are no sign of crater or cauldron of magma. However, the geothermal activities in the form of geysers, fumarole, mudpot, hot spring and steam vent in Yellowstone indicate that there are underground volcanic activities.
There are many geothermal activities in countries like New Zealand, Japan, Iceland. But Yellowstone is one area that holds about 60% of all geysers around the world. The most famous and well known around the world is Old Faithful.
Scientists believed that in ancient time, a super volcano has erupted, and its magma chamber has collapsed forming a huge caldera - the size so huge that the country Singapore can be placed comfortably inside! The collapsed areas gave rise to the beautiful landscape of geothermal geysers with its beautiful colours, as well as the largest lake in US above 2000 m - the Yellowstone Lake.
The Yellowstone National Park is located on average of about 2,100 m and rivers flow down either to the Pacific or Atlantic sides. In this geothermal active zone, bedrocks plunged downward, with other places rising upwards forming the beautiful landscaped mountain ranges. Waterfalls are abundant here, and in one of the lower fall of the Yellowstone River, the rock face is Yellow in colour.
The wall acts like canvas to the Great Artist who created heaven and earth, allows the mineral to stain the wall face. Over time, the various chemical present in the water have stained the canyon walls with palette of Yellow, Pink, White and Red. But in this area, Yellow is most prevalent.
Yellowstone River - Lower Fall
Water flow through the canyon, surronded by Yellow Walls
The surface activities of the geothermal evidences produced many interesting patterns and colours in the various geyser basins.
In the geyser basin, the most famous geyser will be Old Faithful.
Old Faithful geyser - erupt on a regular basis. Geyser occurs when underground chamber contains water that has been boiled to superheated stage (high pressure with high temperature), and because of constriction in one of its chamber, the pressure continues to buildup to the point where the constriction cannot hold back the water, steam, and with a sudden release causes the water and steam to erupt.
Water is of turquose colour, resulted by the dissolved mineral. Mineral in the water calcified on the surface, and forms wall like terrace. 
Volcanic activities are usually associated with toxic substance like sulphur, and in this landscape, rotten egg (Hydrogen Sulphide) is very obvious. The Hydrogen Sulphide rises from the magma, and is consumed by certain bacteria (called thermophiles) thrives in such mudpot, with the byproduct as sulphuric acid. The sulphuric acid “eats” up the rocks and solis, and turn them into mud. Amazingly, some mudpot acidity is so high, that it can easily burn the human skin. 
MudpotUnderground , the water chamber is ever shifting, due to seismic movement. What happen if death to some of the fauna which sheds its leaves and leaving behind a very bald appearance but with a very whitish appearance at the bottom of its trunk - as though it has just put on a white sock! Elsewhere, because of the diversion, suddenly the landscape becomes habitable, and plants started to take root and grow!
In this desolate plain, the ground movement has taken place, and instead of life giving water, the mineral filled water has flown into this area.As a result, the trees in this area have died, and put on a white sock as shown at the base of the trunk. Look carefully, and you can see a lone coyote running in this desolate zone.
However, in area previously was the source of hot spring, the underground channel has shifted, and now grass is beginning to grow in this previously inhospital zone!
Panoramic view of the Hayden Valley.
Look carefully at the river, and you will notice that it is going round in bends.
In time to come, ox bow lake will be formed.
Yellowstone is a most amazing place. Scientists have determined that a major eruption is long overdue from this super-volcano. Much bigger than the Krakatoa in Indonesia. One that will envelope with ashes - turning day into night. One with the potential to split the continent into half.
Yellowstone is a most amazing place. Scientists have determined that a major eruption is long overdue from this super-volcano. Much bigger than the Krakatoa in Indonesia. One that will envelope with ashes - turning day into night. One with the potential to split the continent into half.
Will that day come! While the seismic monitor continue to register the many quakes that occurs, and volcanologists continue in the guest to determine when it will happen.
To us, we will continue to enjoy the great scenery that Yellowstone provides.
Yellowstone River - Upper Fall
Yellowstone River - Upper Fall
Yellowstone River - Lower Fall
