The Excelsior Geyser pool discharges 4,000 to 4,500 gallons (15,100–17,000 l) of 199 °F(93 °C) water per minute directly into the Firehole River. In the late 19th century (there was possibly some activity in 1901 too), it was an active geyser that erupted frequently. Most eruptions were about 100 feet high, but some exceeded 300 feet (91 m) and were as wide as they were high. It is believed that the powerful eruptions damaged its internal plumbing system, and it now boils as a productive hot spring most of the time.
In 1985, Excelsior returned to activity for a 46 hour period from September 14 to 16. These eruptions were relatively small at 30 feet (9.1 m) but a few were as much as 80 feet (24 m) tall and 100 feet wide. All of these eruptions lasted about 2 minutes at intervals of 5 to 66 minutes.
In the mid first decade of the 21st century Excelsior did have violent boiling strong enough to be considered as eruptions, the boiling reached between 5 to 10 feet (1.5 to 3.0 m) and had a duration of seconds.