This Earthcache takes you to small esker. Eskers are long and
narrow ridges that often look like man-made embankments. They were
formed in the last Ice Age, but amongst the glacial landforms they
have become an endangered species.
Eskers were formed by meltwater running through glacial ice
sheets. Glacial ice, unlike what you might have in your freezer,
was all cracked up and full of 'dirt' (sand and gravel picked up as
the glacier spread over the land). Meltwater that gathered at the
top of the glacier flowed off through the cracks, washed out the
sand and gravel, and formed rivers that ran through ice valleys and
ice tunnels in and under the glacier. The sand and gravel carried
along by the water was deposited as sediment at the bottom of these
meltwater flows. When the glacial ice eventually melted away, only
these deposits remained, 'dropped' onto the valley floor carved out
by the glacier. The landscape became inverted: the sand and gravel
that had been at the bottom of meltwater flows now stood out as
ridges, like a river system 'upside down'.
The image below illustrates the formation of eskers. Depending
on whether they form under, on top of, or within the ice sheet,
they are called subglacial (1), supraglacial (2,3) or englacial
(4). It is suggested that only subglacial eskers have an internal
structure with different layers of sediment, whereas other types of
esker do not show stratification.
Esker formation (source:
www.geosite.uni-greifswald.de)
Eskers proved very useful for man. They wind through the
landscape and are made up of well-draining material, which made
them useful as natural pathway, in particular if they had been
deposited on otherwise boggy ground. People also built settlements
close to eskers, as they provided natural shelter. Because eskers
consist of sand and gravel, they were also a very accessible source
of building materials. In fact, they have been quarried so
extensively that they have become nearly extinct.
The esker you will see at the published coordinates is small but
it should let you appreciate how it overlays the shape of the
valley. It is located in a private field and not directly
accessible, except for one end of it which is crossed by a public
footpath. Please note the waypoint for nearest parking. Walk up the
road for about 200m to get to the start of the footpath. Cross
through the field, and then over a stile into the back of a garden.
At the highest point, before the path leads down to the next stile,
find a gap in the hedge on your left. This will give you a good
view of the esker along its spine.
To claim this Earthcache please email answers to the following
questions:
1. Describe the esker as you see it from the published
coordinates: What is the approximate height of the ridge, and in
which direction does it extend?
2. Does the esker run orthogonal or parallel to the valley on
which it has been deposited? What does that tell us about the
meltwater flow relative to the path of the glacier?
3. Under which condition could eskers have formed: when the ice
sheet was advancing, stagnating or retreating? Why would that be
the case?
As usual don’t post your answers in your log. To email us,
click on our name at the top of the page. You do not have to wait
for confirmation from us before logging this cache as
completed.
Hope you enjoy the visit and Happy Caching!
Congratulations to the Quietly Crew for first to visit and
complete this Earthcache.
PS - Cache title is quoting a geological survey of the area, by
T A Hughes (first to find?)