Secrets of groundwater: Thousand Springs State Park and the amazing Snake River Plain Aquifer, Idaho

Main Ideas

Thousand Springs is a major groundwater-discharge area along the Snake River Canyon in south-central Idaho. Clear, cold water emerges from the canyon walls and flows into the Snake River.

The springs are fed by the Eastern Snake River Plain aquifer, a large fractured-rock aquifer hosted mainly in basalt lava flows. Snowmelt and other surface water from central and eastern Idaho seep into the porous, permeable basalt and become groundwater.

Why the Springs Emerge Here

Groundwater generally moves west-southwest, roughly parallel to the Snake River. Near Hagerman Valley and Thousand Springs, the river turns sharply north, bringing groundwater flow into the Snake River Canyon, where it can emerge as springs.

Tracer studies indicate that water may travel underground for about 150–200 years before reaching Thousand Springs. The spring water is cold—about 48°F—and clear.

Geology and Groundwater Pathways

Local geology influences where water can move and emerge. Some basalt is dense and relatively impermeable, while fractures and other connected openings allow water to pass through. Vesicles—small bubbles in the rock—contribute to permeability only when they are interconnected.

The presenter describes two basalt units in the canyon:

• Notch Butte Basalt, about 80,000 years old
• Gooding Butte Basalt, about 373,000 years old

Springs emerge near the base of the Gooding Butte Basalt, above the older Glenns Ferry Formation, a sedimentary unit about 3–6 million years old. Its finer-grained, less-permeable layers act as a confining unit, limiting downward groundwater movement and helping direct water out through the canyon walls.

Pillow basalts also form important groundwater pathways. When lava flows into a river or stream, the water cools it rapidly into rounded or pillow-shaped forms. These pillow lavas tend to be more permeable than the surrounding basalt, making them preferred routes—or “highways”—for groundwater. Springs commonly occur where these features are concentrated.

Regional Importance

Groundwater from Thousand Springs supports hydroelectric power, fish hatcheries and aquaculture, agriculture, and other industries.

Demonstration: Porosity vs. Permeability

The presenter uses containers of gravel and sand to illustrate two related but distinct properties:

• Porosity is the proportion of a material made up of pore spaces. Gravel and sand can have similar porosity and may hold comparable amounts of water.
• Permeability is how easily and quickly water moves through a material. It depends on how well the pore spaces connect.

When water is poured into both containers, it moves through the gravel more quickly because its larger, better-connected spaces provide easier pathways. It moves through the sand more slowly, even though sand can have a similar amount of total pore space, because its spaces are smaller.

Speaker and Sources

Shawn Willsey is the sole speaker and on-site presenter. He explains the aquifer, local geology, and groundwater pathways. No other speakers or external sources are identified in the subtitles.