Giant stair steps
Any accumulation of unconsolidated material (e.g. clay, silt, sand, gravel, cobbles, boulders) deposited by glacial ice; an
accumulation of till. Till refers to material deposited by glacial ice. Thus moraines are composed of till. There are several
types (classes) of moraines with different appearances and characteristics. Scientists classify moraines based either on where
the till is deposited relative to the glacier (e.g. beneath the glacier, in front of the glacier, along the side of the glacier)
or on the mode of deposition (e.g. material released as ice melts, material smeared onto the underlying land surface). Where
the sediment is deposited relative to the glacier and the mode of deposition determines the appearance and characteristics of
Regardless of the moraine class, one characteristic all moraines share is that the till (or rock debris) comprising
moraines is unsorted. Unsorted means that different sizes of sediment are all mixed together; the very small and the very
large and everything in between is jumbled together. If the deposits were sorted, this would mean that all the small-sized
particles were deposited in one location, the medium-sized particles in another location, and the large-sized particles
elsewhere. Sorted deposits may show layering, with a particular particle size comprising each layer. Moraines do not show
layering. Sorted deposits may show a progression from smaller-to-larger or large-to-smaller particles over space (from one
end of the deposit to the other end of the deposit). Moraines do not show a progression of grain size from one end of the
deposit to the other end. Thus moraines, regardless of class, exhibit no sorting.
The photo to the right shows the unsorted sediment (till) of an end moraine. Although the smaller-sized particles are not
readily visible, you can still see many different sizes of clasts in the moraine. If you dug into the till, you would probably
find sand, silt and clay in addition to the larger clasts that are clearly visible in the photo.
Photo: P. Carrara. 1979. USGS Photographic Library, photo car00302. <http://libraryphoto.cr.usgs.gov/> Accessed June 2010.
Four basic types of moraines associated with alpine glaciers include end moraines, ground moraines, lateral moraines, and medial
moraines. These moraines are part of the classification based on where the till is deposited relative to the glacier. Click on the
term in the list to the left to see definitions and examples of each of these types of moraines.