File:Emerald Spring (9 August 2011).jpg

English: Emerald Spring, northern Back Basin, central Norris Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA on 9 August 2011 (looking ~WSW).

This 25 to 30 feet deep pool has occasional geyser eruptions, but is usually a gently overflowing hot spring. The water is acidic and near-boiling to superheated. The intense green color is a combination of blue, colloidal silica-rich water (seen in many, very hot pools throughout Yellowstone) and yellow-colored elemental sulfur (S) lining the floor and walls of the pool. A thin border of whitish-colored siliceous sinter, composed of opal (SiO2·nH2O - hydrous silica), encircles the pool.

A rising stream of bubbles near the center of Emerald Spring consists of water vapor (H2O), carbon dioxide (CO2), plus other gases. A whitish- to grayish-colored, siliceous sinter-lined runoff channel heads southwest from Emerald Spring (see upper left of photo), merges with Monarch Geyser’s runoff channel, and eventually drains into Tantalus Creek.

In the early 1930s, Emerald Spring had significant and frequent geyser eruptions up to about 80 feet high.

During the annual Norris Geyser Basin disturbances, Emerald Spring becomes muddy (= suspended fine-grained sediments) and has relatively small geyser eruptions about 6 feet high or less.