Mars Astrobiology: Recent Status and Progress - Planetary Exploration and Science: Recent Results and Advances - page 166

These scalloped features are superficially similar to “Swiss cheese” features,
found around the south polar cap. “Swiss cheese” features are thought to be due
to cavities forming in a surface layer of solid carbon dioxide, rather than water ice -
although the floors of these holes are probably H 2 Orich.

8.3.5.6 Glaciers

Many large areas of Mars either appear to host glaciers or carry evidence that they
used to be present. Much of the areas in high latitudes, especially the Ismenius
Lacus quadrangle, are suspected to still contain enormous amounts of water ice.
Recent evidence has led many planetary scientists to believe that water ice still
exists as glaciers across much of the Martian mid- and high latitudes, protected
from sublimation by thin coverings of insulating rock and/or dust.
In January 2009, scientists released the results of a radar study of the glacier-like
features called lobate debris aprons in an area called Deuteronilus Mensae, which
found widespread evidence of ice lying beneath a few meters of rock debris. Glaciers
are associated with fretted terrain and many volcanoes. Researchers have described
glacial deposits on Hecates Tholus, Arsia Mons, Pavonis Mons, and Olympus Mons.
Glaciers have also been reported in a number of larger Martian craters in the mid-
latitudes and above.
Glacier-like features on Mars are known variously as viscous flow features,
Martian flow features, lobate debris aprons, or lineated valley fill, depending on
the form of the feature, its location, the landforms it is associated with, and the
author describing it. Many, but not all, small glaciers seem to be associated with
gullies on the walls of craters and mantling material. The lineated deposits known
as lineated valley fill are probably rock-covered glaciers which are found on the
floors of most channels within the fretted terrain found around Arabia Terra in the
northern hemisphere. Their surfaces have ridged and grooved materials that deflect
around obstacles. Lineated floor deposits may be related to lobate debris aprons,
which have been proven to contain large amounts of ice by orbiting radar. For many
years, researchers interpreted that features called “lobate debris aprons” were glacial
flows, and it was thought that ice existed under a layer of insulating rocks. With new
instrument readings, it has been confirmed that lobate debris aprons contain almost
pure ice that is covered with a layer of rocks.
Moving ice carries rock material and then drops it as the ice disappears. This
typically happens at the snout or edges of the glacier. On Earth, such features would
be called moraines, but on Mars, they are typically known as moraine-like ridges,
concentric ridges, or arcuate ridges. Because ice tends to sublime rather than melt
on Mars and because Mars' low temperatures tend to make glaciers “cold based”
(frozen down to their beds and unable to slide), the remains of these glaciers and
the ridges they leave do not appear to be exactly same as normal glaciers on Earth.
In particular, Martian moraines tend to be deposited without being deflected by the
underlying topography, which is thought to reflect the fact that the ice in Martian
glaciers is normally frozen down and cannot slide. Ridges of debris on the surface