490 Students on Nea Kameni
The centre of the Thera caldera is occupied by two low basaltic volcanoes known as the Kamenis. Palea (ancient) Kameni which first is recorded in Roman times, has a younger volcano, Nea (new) Kameni on its eastern flank. Nea Kameni's last major eruption was in 1926, although the volcano also exhibited activity from 1939 to 1941 and in 1950. This class photo was taken at the summit of the 1950 crater looking toward the north. The remnants of the caldera rim can be seen on the far left and right sides of the photograph. More on Thera in the next issue ofWat on Earth!
© Alan V. Morgan
If you were asked to associate a country and its geology it would be relatively easy for Iceland - ice and fire, glaciers and volcanoes. The United States? Well, perhaps Yellowstone and the Grand Canyon - geothermal and sediments; Japan? um, earthquakes and volcanoes? Greece? Karst topography and marble, oh, and perhaps earthquakes!
In September 1994, 17 students and two professors left Waterloo to find out whether this perception was true. Two weeks later, after much sunshine, some ouzo, and lots of superb geology we found that it was true, but there was so much more!
Space precludes anything but highlighting a few aspects of what went on on the Greek fieldtrip. It all started in Athens, barely metres away from the back of the National Museum where we had gathered in a small (and cheap) hotel. Culture shock for many of our students who were used to the rigors of frigid work terms on frozen lakes in Newfoundland or the dust of section roads in western Canada, but not equipped for a different language and, perhaps even more disconcerting, a different alphabet! Mousaka and Baklava were familiar to some, but reading road signs to get out of Athens?
The following day saw us leaving the city (fortunately only a few turns and "straight ahead") and we were soon on the new expressway heading north to Thebes, located on the margin of the Kopias Basin, formed by recent block faulting. The rocks here are limestones and dolomites with interbeds of shale, siltstone and sandstone, and ophiolites (peridotities, diabases and gabbros). The basin is lined by lacustrine clay.
The limestones contain many caves and sinkholes concentrated along the sub-vertical faults that border the basin. The ancient Thebans tried to block the sinkholes to flood the basin and destroy the agriculture of Orchomenos in the days of classical Greece. In 1311 the Catalans defeated their enemies in the same manner, by blocking the sinkholes and flooding the battlefield and encampments (brings a whole unexplored dimension to groundwater geology!). The shallow lake was drained during 1886-1931 by a tunnel and drainage trenches. The nearby Lake of lliki has recently been used as a source of water for Athens, but, unfortunately, as we were to see over the next few days, nowhere near enough to handle the demands of a growing metropolis, and the millions of tourists visiting Greece.
A few hours later we were at Delphi, long famous for the Delphic sanctuary including the earth goddess Gea (Gaia), and also Poseidon, and Apollo (and a few lesser-known deities). Delphi is within the Corinthian seismic area and suffers from earthquakes as well as acid rain, pedestrian traffic, and other ills. In March 1985, after heavy rains, a large rock fall damaged the temple of Athena Pronea. At the Kastalia Spring, wedge-slides and rock falls from the higher slopes endangered the site and were fenced off. Investigations showed the slopes to consist of limestone and flysch with a talus deposit at the base. The rocks are faulted and folded, with overturning and inverse stratigraphy at some locations. In the parking area, the investigations uncovered near-vertical joints with an average aperture of 10 cm, and one large joint with aperture 1.0 to 1.5 m filled with sandy sediments. The potential toppling situation was monitored by installing instruments across some of the open cracks. Stability calculations indicated low factors of safety. Rock anchors were installed and grout injected to fill open joints and reduce the water pressures. Extemal retaining walls, beams, etc., were avoided for aesthetic reasons.
From Delphi the road descends precipitously to Itea cutting through limestones and dolomites up to 1,500 m thick, as well as three horizons of bauxite. Intense karstic solution has created very large springs, both inland and coastal with flows of up to 7,000 m3/hr. The Kirra Spring at Itea flows at 5,000 m3/h and contains 30% sea water.
Our first real working day involved a visit to the Mornos Dam and aqueduct, part of an ongoing struggle to keep Athens supplied with water, and a problem which we were to see again the following day. The Mornos dam has a central clay core and transition zones and outer shells of sand and gravel. The upstream slope is protected by rip-rap, and the downstream slope by shrubs. The water supply is completed with a 186 km long aqueduct carrying water from Mornos to Athens. The aqueduct includes 14 tunnels of a total length of 67 km as well as a number of siphons and canals. Construction was completed during 1969- 1979. The dam and much of the reservoir are on a flysch sequence of rhythmically interbedded shales and sandstones. Karstic limestones are present at some locations, and provided some fascinating scenarios for our engineering and groundwater geologists. For example, the longest section of aqueduct tunnel runs 14.7 km beneath the Giona Mountains from the Mornos dam, east to Amfissa. Both portals were in flysch but the main part of the tunnel was excavated through karstic limestone, including about 10 faults and two karstic conduits. The first karst was empty and produced large inflows at first, but the flows quickly receded. The second karst, full of silty sand and gravel, was dry when first intercepted but flooded the tunnel eight hours after a storm. This water took a week to drain away. Around the dam the perimeter slopes at Mornos were stabilized by removal of material from the slope crests and by drainage. The reservoir was mostly watertight. Limestone occurred as inliers on impervious flysch except for a 2.5 km highly jointed and karstified strip of limestone about 6 km east of the dam. Here, sand and gravel were compacted to provide a smoothly sloping surface which was then paved with 236,000 square metres of asphalt.
The following day we went on to the Evinos Dam, a new dam under construction to the west of Mornos and again designed to funnel water to the thirsty inhabitants of Athens. A 50 km drive (only 15 km as the crow flies) brought us to where a 100m high embankment dam is under construction on the river Evinos, near the village of Agios Dimitrios. The bedrock is weathered flysch with varying degrees of folding and in some places complete destruction of the rock.
The dam is on flysch close to its contact with the underlying limestones. The flysch is particularly disturbed in the abutment where the diversion and spillway structures are located. Sharp folding cannot be maintained through the thickly-bedded sandstones. Sliding and shearing of beds occurs, particularly close to the axes of folds. Pieces of broken sandstone and siltstone are found "floating" in sheared weaker siltstone and shale. Rock-like slab and wedge slides can occur in the more competent flysch, whereas circular slips, typical of soils, are more likely in the more weathered and strongly disturbed zones. One such example, which happened during torrential rains less than one month before our visit, created a spectacular example of a rotational shear slump with a circular, beautifully striated backface and a roadway which had been broken and fissured with cracks several metres deep.
Our visit to the dam was a day of celebration since the tunnel-boring machines (TBM's) had just completed the Evinos-Mornos tunnel, a 29 km long excavation through the Pindus range. The rock consisted of Triassic to upper Cretaceous carbonates and silicates overlain by deposits of Eocene flysch. The tunnel started at Agios Dimitrios, where it was excavated by unshielded TBM and supported by NATM (new Austrian tunnelling method), passing from flysch to limestone through a tectonic thrust zone with moderate water inflow. The TBM advanced at 30-47 m per day in the better quality rock, 10-20 m per day in inferior rock, and well under 10 m per day for a distance of 260 m through the chert.
It was a well-fed group that finally left broke away from a superb afternoon meal at Evinos for the rather hair-raising trip back across the mountains and valleys to Nafpaktos, and, the following day to Ioannina and then Meteora.
I have been to Greece on many occasions and yet Meteora always comes as a surprise. The region is in the mid-Hellenic trough and contains sedimentary rocks deposited during the Oligocene and Miocene, including more than a 5 km thickness of molasse-type sediments. Gentle folding during the early Miocene was followed by more recent and severe faulting, forming a series of horst and graben structures. These faults as well as the ease of weathering of some units of the sediments have contributed to the spectacular Meteora scenery. The formations from the top down include the Tsotylion (marls, sandstones, conglomerates, etc.), the Pentalofon (interbedded hard and soft conglomerates and sandstones), the Eptahori (blue-grey marls and calcareous siltstones and mudstones) and the Krania flysch lithology (thinly interbedded shale and sandstone).
The monasteries of Meteora rest on pinnacles of easily eroded sedimentary rock of the Tsotylion, Pentalofon and Eptahori formations. Known locally as the "Stone forests" of Meteora, these impressive rock columns in the terminology of the Grand Canyon and Arizona would be called mesas and buttes.
From Meteora we continued east towards the Plains of Thessaly and to Thermopylae where Leonidas and his 300 Spartans went to their fate in combat with the Persian army, but more on this, and the conclusion of the trip in the next issue of Wat on Earth.
Alan V. Morgan