Thundering Waters - Oregon Cascade Falls User Guide
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Bureau of Land ManagementUnited States Forest Service
The Way Water Falls

How do waterfalls form? The Cascade Range is made of volcanic layers from numerous eruptions over the last 35+ million years. The layers, or deposits, originated from numerous sources, each having a different resistance to erosion. They were then uplifted after the volcanic activity stopped. The stream’s erosive energy continues to carve the channels that we see today.

Waterfalls develop when downcutting streams breach through a resistant bedrock layer into the softer material beneath. The height of the waterfall is dependent upon the thickness of the resistant bedrock layer through which the stream erodes.

Do waterfalls change? Energy from plummeting water creates a plunge pool at the base of the waterfalls, eroding a cavity in the softer underlaying rock. This process undermines the resistant layer, causing it to break apart, piece by piece, along cracks and fissures. Through this process, waterfalls gradually migrate upstream. Over the course of thousands of years, this movement can be a few to several feet.

Are there different types of waterfalls? Water plummets over ledges of basalt in eight forms. While most falls have elements of more than one form, the examples shown are most representative of each type.

Hemlock Falls Hemlock Falls
Hemlock Falls
Cascade Type
Follows along a series of rock steps
Segmented Type
Descends as the stream diverges into 2 or 3 parts
Block Type
Descends from a wide stream
Tiered Type
Descends from a distinct series of seperate falls
Punchbowl Type
Descends from a constricted width of a stream into a pool below
Plunge Type
Descends vertically, losing contact with the bedrock below
Horsetail Type
Descends vertically maintaining some contact with the bedrock surface
Fan Type
Similar to horsetail form, with an increasing width of spray

**Information adapted with permission from the Waterfall Lover's Guide to the Pacific Northwest, by G.A. Plumb, The Mountaineers, Seattle, WA.


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