Penta Geyser

Overview

Tucked into Geyser Hill in the Upper Geyser Basin, Penta Geyser sits just off the boardwalk beside Spasmodic and Sawmill Geysers. True to its name, it has five vents. When it wakes up, you’ll see clustered bursts that can reach about 25 feet and keep going for 30 minutes to 2 hours, sometimes even twice a day. It’s a great “linger and watch the plumbing” spot—when it’s in the mood.

How It Behaves (and Why It’s Fickle)

• Penta’s activity is tightly linked to the Sawmill Complex. It often starts when water levels in the area rise and Spasmodic (sometimes Tardy) is already erupting.
• If Sawmill kicks on during Penta’s preplay, it can drain the system and shut Penta down before it really gets going.
• It usually erupts alongside Spasmodic and tends to end a few minutes after Spasmodic stops.
• “Modes” matter: in the “Penta–Churn” mode, you might see daily action; in the more common “Sawmill” mode, Penta can be rare.
• Historic note: it’s been nicknamed “the Handsaw.”

What to Look For

• Watch Penta’s pool fill and overflow toward Sawmill—good sign an eruption window is near.
• Keep an eye on Spasmodic: if it’s going strong, Penta often joins the show; if Spasmodic quits, Penta may wind down soon after.

Getting There & Amenities

There’s no dedicated lot or restroom at Penta. Park at the Old Faithful/Visitor Center area and walk the Upper Geyser Basin boardwalks to Geyser Hill. Expect to rely on the facilities in that main hub area.

Best Time to Visit

There isn’t a dependable schedule here. Your best bet is to swing by while exploring Geyser Hill and linger when Spasmodic is active and Penta’s pool is rising. Conditions and temporary closures can change quickly—check day‑of advisories and be flexible.

Safety

Stay on the boardwalks, supervise kids, and treat every thermal feature as dangerously hot.

For the Curious

At the vent, water runs roughly 185°F with alkaline chemistry (around pH 8.7) and notable conductivity—classic signs of a robust hydrothermal system powering those five vents.