Introduction

 

Yellowstone National Park is a world class example of a region that has resulted in significant volcanic activity. Weathering and erosional processes have created surface expressions that are unique and spectacular in natural design. There have been three major caldera-forming mega-volcanic eruptive events throughout the Yellowstone region spanning the past 2.1 million years. These major eruptions occurred as the Huckleberry Ridge Tuff (2.1 million years ago), Mesa Falls Tuff (1.3 million years ago), and Lava Creek Tuff (631,000 years ago). The most current Yellowstone caldera is the result of the Lava Creek Tuff episode and spans an area of 30 by 45 miles (50 by 70 kilometers). Yellowstone Park covers 3,472 square miles while the caldera’s area is 1,350 square miles, approximately thirty percent of the area of the park.

 

Since the actions of the Lava Creek major eruptions, several smaller scale volcanic eruptions have occurred. At least eighty non-explosive events deposited layered volcanic breccias, conglomerates, rhyolitic and andesitic lava flows, lahars, mud and debris flows, and interbedded sandstones. These more recent deposits are included within the Absaroka Volcanic Supergroup which developed between 53 and 43 million years ago (middle Miocene Epoch).

 

The volcanic deposits photographed on these pages are exposed along an eighty-miles stretch from the Fishing Bridge intersection in Yellowstone National Park to Cody Wyoming. The source for many of these deposits can from the Sunlight Volcano about twenty miles north. The diameter was estimated to be about twenty-five miles, and it was active from about 50 to 48 million years ago.