Giantess Geyser

Overview

Giantess Geyser is one of the Upper Geyser Basin’s heavy hitters—when it wakes up. It’s a powerful fountain-type geyser with rare but thunderous eruptions that can shoot water well over 100 feet. You view it from established boardwalks near Old Faithful.

What You’ll See

When quiet, Giantess is a large, deep pool with a constantly boiling center. Thin, pale sinter rims the edges, and the runoff channel often glows with orange thermophiles. Before big shows, the ground may rumble from underground steam activity, and when it goes, it can throw repeated bursts and then settle into a prolonged steam phase.

Eruptions and Activity

This geyser is the definition of fickle—some years it doesn’t erupt at all; other years have logged dozens of events. Eruptions are typically infrequent and unpredictable, but when an episode starts it can continue on-and-off for 4 to 48 hours, with bursts sometimes reaching 100–200 feet. There are no reliable predictions; check with rangers for current observations.

Geology in a Nutshell

Rain and snow percolate thousands of feet underground and are heated by magma a few miles beneath the surface. Constrictions in the geyser’s plumbing trap water and steam until pressure forces an eruption. Giantess appears to be connected to neighboring hydrothermal features, and its pool chemistry skews alkaline (around pH 8.1) with average temperatures near the boiling point for Yellowstone’s elevation.

Safety Essentials

Stay on boardwalks and designated trails—thermal ground is thin and the water can cause severe burns. Supervise kids closely and never step on the colorful runoff channels or microbial mats. Wildlife sometimes crosses thermal basins; give bison and elk plenty of space (and even more for predators) and never block their path.

Best Time to Visit

There’s no “timed” visit for Giantess. If rangers or fellow visitors report activity, go immediately—episodes can last hours to nearly two days, so you may still catch part of the show. Otherwise, treat it as a bonus while you explore the Upper Geyser Basin boardwalks.

Getting Oriented

You’ll reach Giantess via the Upper Geyser Basin boardwalk network near Old Faithful. There’s NPS signage along the paths, but no services at the pool itself—use the developed facilities in the Old Faithful area.