The Yellowstone Volcano Observatory (YVO) reported that on 23 July a hydrothermal explosion occurred at Yellowstone’s Black Diamond Pool in the Biscuit Basin thermal area. The explosion ejected a plume of water, mud, and rock fragments 120-180 m high and NE towards Firehole River. Some ejected boulders were more than a meter in diameter. A section of the boardwalk to the S of the pool was notably damaged. The area, including the parking lot and boardwalks, was closed to visitors after the explosion. Hydrothermal explosions are relatively common in Yellowstone; on average, there are a few of varying sizes somewhere in the park each year, often in the backcountry where they may go unnoticed. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest color on a four-color scale).

Geological Summary. The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years that included some of the world's largest known eruptions. Eruption of the over 2,450 km3 Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera. The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the over 1,000 km3 Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 km3) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have occurred since the late Pleistocene, but large hydrothermal events took place near Yellowstone Lake during the Holocene. Yellowstone is presently the site of one of the world's largest hydrothermal systems, including Earth's largest concentration of geysers.

Source: Yellowstone Volcano Observatory (YVO)