- Lahar
- Lakes
- Land and Sea Breezes
- Landforms
- Landscape Evolution
- Landslide
- Laterite
- Latitude and Longitude
- Lava
- Leaching
- Lead
- Lehmann, Inge (1888-1993)
- Libby, Willard F. (1908-1980)
- Lightning
- Limestone
- Lineation
- Linné, Carl von (1707-1778)
- Lippershey, Hans (1570-1619)
- Lithification
- Lithosphere
- Lithospheric Plates
- Longshore Drift
- Lyell, Charles (1797-1875)
