is formed as waters erupt from a hot spring into environments
characterised by sub-zero air temperatures. This process has been
overlooked in previous investigations of the sedimentology of hot spring
areas such as Yellowstone, Iceland and El Tatio in Chile all of which
are subjected to either seasonal or daily freezing cycles. In all of
these areas a considerable volume of sediment accumulating each year on
sinter aprons and in geothermally influenced wetlands has passed through
a freezing step prior to deposition.
first became aware of the presence of such sediments during
investigations of a small geothermal wetland at Porkchop Geyser,
Yellowstone National Park. The strange morphology of some of the
particles within this wetland appeared to be impossible to form during
"normal" summer silica precipitation processes.
breakthrough moment in my investigations of these particles came when I
found images of the microstructure of sea ice. Resin impregnation of
blocks of ice reveal a network of brine channels, veins and pockets that
form as salt dissolved in the water prior to freezing is excluded from
incorporation in forming ice crystals. In hot spring areas silicon is
present in solution along with salt. It is also excluded from ice
crystals. As it is present at supersaturated concentration it
precipitates in the brine channel network.
Hot spring environments in Yellowstone with hot spring ice and cryogenic opal-A sediments.
In 2006 I was awarded an Earth and Space Foundation Award that part funded my investigations of cryogenic mineral formation around terrestrial thermal springs.
The project funded was entitled -
Astrobiological implications of hydrosphere, cryosphere, biosphere interactions at Icelandic hot springs
Category: Using environments on Earth to understand other worlds / exobiology
Institution: Cardiff University, Edinburgh University.
depositing hot springs are prime astrobiological targets because on
Earth hot springs support abundant microbial populations which are
fossilized by minerals precipitating from their spring waters.
Fossilization creates rocks with identifiable structural and/or
molecular markers for biological activity which are durable over
geological timescales. Increasingly, frozen environments (cryosphere)
are also seen as potential havens of extraterrestrial life. This
project aims to explore interactions at the interface between the
biosphere, cryosphere and hydrosphere in a Mars-like setting. Martian
hot spring systems are most likely to be “rooted” in basaltic crustal
rocks, this would favour the formation of mixed silica, carbonate and
iron oxide hot spring deposits at the Martian surface. Of Earths' major
geothermal areas Iceland which has basaltic volcanism provides the
closest analogue to this setting.
Specifically this project aims to:
by field observation the extent to which cryogenic conditions influence
mineral precipitation processes at Icelandic springs and investigate
processes that influence their formation and distribution.
the hypothesis that microbial fossilisation is associated with mixed
mineral phases generated by cryogenic processes by collection of
geothermal water samples, ice samples containing cryogenic precipitates
and cryogenic sediments for analytical and microscopic investigations.
the idea that microbes may survive sequentially being immersed in hot
spring water and then supercooled extremely saline water in brine
channel environments by attempting to culture microbes from hot spring
Natural and synthetic cryogenic opal-A particles respectively collected
from Yellowstone N.P. and created at Cardiff University.
Collecting cryogenic opal-A from beneath hot spring ice on the sinter apron of Strokkur Geyser, Iceland.