Weathering on Half Dome: The Exfoliation Masterpiece

Yosemite's Iconic Dome Is a Weathering Product

Half Dome's smooth, rounded crown isn't carved by glaciers alone—it's a textbook example of exfoliation weathering in granitic rock.

The Process: Sheet by Sheet

1. Deep Origin: Half Dome's granite (Half Dome Granodiorite) crystallized ~87 Ma at ~5–10 km depth under high pressure.
2. Uplift & Erosion: Overlying rock removed → pressure release → rock expands.
3. Fracturing: Expansion creates sheet joints (exfoliation joints) parallel to the surface—concentric "onion skin" fractures.
4. Water & Ice Wedging: Water enters joints; freeze-thaw cycles pry sheets apart.
5. Thermal Cycling: Daily heating/cooling expands/contracts surface layers, fatiguing rock along joints.
6. Sheet Spalling: Curved slabs (cm to meters thick) detach and slide off, exposing fresh, unweathered rock.

Why the Dome Shape?

• Joints follow the topography of the intrusion's roof—a broad, convex upward bulge.
• As sheets peel, they preserve the curvature, creating the smooth dome.
• Glaciers (Sherwin, Tahoe, Tioga) scoured the flanks (creating the sheer NW face) but the crown is primarily exfoliation.

Mineral-Scale Weathering

Granite = quartz + feldspar + biotite + hornblende.

• Feldspar & biotite: Chemically weather to clay; crumble.
• Quartz: Resistant; remains as sand grains on dome surface.
• Result: Gritty, quartz-rich surface—great friction for climbers' shoes.

Active Today

Exfoliation continues. In 2015, a ~200-ton sheet fell from the Regular Northwest Face route. The dome is alive, slowly shedding its skin.

See It Yourself

Hike the Cables Route (permit required) or view from Glacier Point, Washburn Point, or Olmsted Point. The curved, sheet-jointed crown is unmistakable—geology written in stone.