Yellowstone Caldera Size Is Overstated
On the Sunday, January 4, 2009 Coast To Coast AM With George Noory, Mitch Battros, a self-proclaimed “expert” on earth changes (Whatever that means.) and self-published author of the book “Solar Rain” stated the eruption of the Yellowstone Caldera would be 10,000 times that of the Mount St. Helens eruption.
A quick factcheck reveals that:
the 1980 eruption of Mount St. Helens ejected 0.3 cubic miles (1.2 cubic km) of material,
the Yellowstone Caldera eruption occurred 640,000 years ago and produced 240 cubic miles (1,000 cubic km) of material.
Some quick math reveals 240 / 0.3 = 800 (1000 / 1.2 = 833). That’s an error that is off by roughly a magnitude.
What’s a magnitude between friends? Who cares about an error of a magnitude? It’s like driving 8 miles over the speed limit and having the police officer giving you a ticket for driving 100 miles over the speed limit.
Toba Caldera Size Is Overstated
Mitch Battros said that Toba, an Indonesian volcano that erupted about 75,000 years ago, was about 10,000 times the size of Mount St. Helens.
Wrong again. It is estimated that Toba released about 2,800 cubic km of material. Again doing the arithmatic we have 2800 / 1.2 for about 2333 times the size of Mount St. Helens. Closer then before but still not even close to the 10,000 figure Mitch Battros gave on the show. And he knew he was going onto the show to talk about volcanos.
||Amount of Material Ejected
||Times the size of Mt. St. Helens
|Mount St. Helens
||May 18, 1980
| * VEI is an exponential scale
** Thought to be the largest volcanic eruption in the last 25 million years.
Mitch caldera description
Mitch describing a caldera said, “Imagine a volcano that is unside down. That really does help describes how a caldera actually works. The top of the volcano does not have a typically cone that we would imagine such as volcano Taupo (?) Mount St. Helens or any number of volcanoes that have this high rise that comes to a peak. A caldera is underground. So really from a visually point of view, if we were to stand there, such as Yellowstone, and looked across, we wouldn’t notice anything other then the geophysical events that are occuring, the thermal events. So the vast portion of a caldera is below the surface and it goes down, tunnels down to magma chambers. [Editor note: This is true of all volcanoes when you include the magma chamber.]”
The Glossary of Geology defines a caldera as “a large, basin-shaped volanic depression, more or less circular or cirquelike in form, the diameter of which is many times greater than that of the included vent or vents, no matter what the steepness of the walls or form of the floor.” 
Ritter says caldera depressions are formed when “eruption spews forth large quantities of material, creating an empty space in the underlying magma chamber. This results in an inward collapse of the upper part of the volcanic cone, often along fractures that develop following the eruption.” 
Ritter goes on to clarify that the primary distinction between a normal volcanic crater and a caldera is one of size with one mile (1.6 km) diameter being the dividing size.
In other words, a caldera is simply the remains of a supervolcano. What a crater is to a normal volcano, a caldera is to a super-volcano.
The cross-sections above show a stratovolcano during eruption and afterwards. The general profile of the volcano remains the same — steep sides with a distinct crater on top.
Supervolcano and its Caldera
The images below show the sequence of forming a caldera
Because of the large size of the vacated space* in the magma chamber, the chamber collapses under the weight of the overlying rock. This causes an enlarge crater called a caldera to form. Often a lake will form within the caldera.
In the left image at very top of the page the Yellowstone caldera rim can be seen in the distance. The image is of the northeastern part of the Yellowstone Caldera with the Yellowstone River flowing through Hayden Valley in the interior of the caldera.
*Technically the chamber isn’t really empty. The expelled materials causes the magma chamber to have less interior pressure. With the lower pressure, the chamber can no longer support the overlying rock load.
 Bates, Robert L. and Jackson, Julia A., Editors; Glossary of Geology, 3 rd Edition; American Geological Institute; Alexandria, Virginia; 1987.
 Dale F Ritter; Process Geomorphology; Wm. C. Brown Publishers, College Division; Dubuque, Iowa; 1978, 1986; Page 50.
Supervolcano images modified from:
Williams, Howell; Crater lake: the story of its origin; University of California Press; Berkeley, California, USA; 97 Pages; 1941.