Geology Reference
In-Depth Information
Julius Büdel (1982, 345) believed that human activ-
ities caused the changes in fluvial activity. He argued
that the fairly uniform conditions of the Alphéios bed
from about 1000
BC
to
AD
500 reflected a long period of
political and agricultural stability. The phase of medieval
alluviation, he contended, stemmed from the destruction
of a well-ordered peasant agriculture, the lapse of a scared
truce that allowed people from a wide area to flock to the
Games every four years, and an exodus of the populace to
safer areas. However, this argument seems the wrong way
round: while the population of the area was rising and the
land was used more intensively, the landscape was stable,
but once the population declined erosion set in (Grove
and Rackham 2001, 292). A scrutiny of the wider region
of Olympia places the question of erosion in a different
perspective (Table 14.2). First, the Ládon, a tributary of
the Alphéios, connects through underground passages to
Phenéos, a large karst basin. The underground channels
block and unblock owing to earthquakes and the washing
in and out of trees from the surrounding forests. When
blocked, a lake forms in the Phenéos. If the lake should
reach 100 m before decanting, the catastrophic discharge
would uproot trees in the Ládon and Alphéios valleys and
carry them downstream. Gravel-pits near Alphioússa,
5 km downstream from Olympia, contain tree trunks
with roots attached, some lying about 2 m below the
surface and some on the surface, the latter being radiocar-
bon dated to the last 300 years. Second, a site at Górtys,
which lies on an upstream tributary of the Alphéios,
shows three phases of slope erosion and alluviation: pre-
historic, early Byzantine, and several centuries later. This
additional evidence shows the complexities of invoking
a single cause for alluviation in all catchments. On the
Alphéios, at least two catastrophic events dislodged huge
quantities of gravel, uprooted trees, and carried them
downstream. These events little affected the Kládheos,
although the Alphéios gravels could have encouraged
the trapping of finer sediment in the Kládheos. Near
Górtys, on the Loúsios river, a tributary of the Alphéios,
two phases of historical deposition occurred, each fol-
lowed by downcutting. Given the tectonic instability of
this region, it is perhaps not surprising that different
areas suffer massive erosion at different times (Grove and
Rackham 2001, 295).
Alluvial history of the Mediterranean
valleys - climatic change or human
malpractices?
Chapter 1 (p. 9) described Claudio Vita-Finzi's classic
work on the history of alluvial fills in the Mediter-
ranean valleys. Vita-Finzi recognized two chief fills -
an Older Fill produced under glacial conditions, and a
Younger Fill produced by episodes of erosion from later
Roman Imperial times to the Middle Ages. Vita-Finzi
attributed both these fills to changing climatic regimes.
Other workers point to human activities as the primary
cause of the Younger Fill. Explanations for the Medieval
Fill in the area around Olympia, Greece - the site of the
ancient Olympian Games - illustrate the arguments for
climatic versus human causes.
Olympia sits to the north of the Alphéios valley where
the Kládheos stream enters (Figure 14.4; Plate 14.2). The
sacred site of Altis lies just eastward of the Kládheos,
close to the foot of Kronos hill. Excavations at the site
revealed stone buildings, including the Temple of Zeus,
a Hippodrome, and a Byzantine fortress. The archaeo-
logical remains lie beneath 5-6 m of silt, which appears
to have begun accumulating after
AD
600. In antiquity,
the Kládheos stream seems to have occupied a lower level
than it does today, a basal conglomerate, possibly of early
Pleistocene date, indicating its bed. A pipe built during
the reign the Emperor Hadrian in
AD
130 to drain the
athletes' baths, the kitchens, and the sanitation facilities
could not have functioned without sewage backing up
unless the average levels of the Alphéios and Kládheos
were about2mlowerinantiquity than today (Büdel
1982, 343). During the deposition of the Medieval
(Younger) Fill, the Kládheos flowed at a higher level than
today, its floodplain burying the Olympian ruins and
the Byzantine fortress. Some time after the Medieval Fill
ceased forming, possibly in the fourteenth or fifteenth
century, the Kládheos cut down to near its original level,
breaching a Roman confining wall now mainly on its west
side. At the same time, the Alphéios shifted northwards,
eating into the remains of the Hippodrome and forming a
cliff in the tail of the Kládheos sediments that defines the
edge of a Medieval terrace (Figure 14.4). These changes
seem to have stopped by the mid-eighteenth century.
