The natural landscape of the area now occupied by Cambridge has been evolving
for millions of years. The main agents of this change have been the freezing
and thawing of soil during the intense cold of the Ice Ages and the action
of rivers that have been removing this material and progressively cutting
into the landscape.
Rivers carrying gravel, sand and mud at times of flood
have built flat 'terraces' or floodplains using some of the material they
have transported. In Cambridge, rivers have created a 'staircase' of terraces,
each relating to a specific period, which together represent over 400,000
years of landscape change. The river terraces preserve evidence of past
climatic conditions that allow the reconstruction of past Cambridge environments.
On this walk we will visit various localities where it
is possible to see stages in this process of lowering of the land-surface,
where terraces at different levels are relicts of several different ancestors
of the River Cam. These ancestors flowed in different directions, with
different styles of river behaviour and different plants and animals on
their banks, because of the way the landscape and the climate was changing.
Rivers generally vary greatly in their appearance, depending
on the amount of water they are carrying, the type of material (gravel,
sand and mud) available, and the gradient of the valley down which they
are flowing. Under present conditions and without interference by humans,
the River Cam would be a quietly flowing stream with a single meandering
river channel and muddy banks. At times in the past, under Ice Age conditions,
the river has been much more violent when rapidly melting-snow and ice
caused floods that covered large areas of the valley floor with gravel
and sand, so that many river channels picked their way between gravel
islands, giving it a "braided" appearance.
On this walk you will also see a variety of wildlife
such as ducks and swans with the potential sighting of moor hens, bats
and pike. There is also a a wealth of flora to be found on the route -
from a wide variety of trees to the exotic plants in the college gardens!