3. GEO Assign 2 (Catas.)

HORIZONTAL LANDSLIDES

Mass Movements in Level Areas [Catastrophism Geology] Year 1 No. 2 (Dec 1976)
_A water satur[at]ed soil layer may turn into a liquid, when it receives a shock, this process is called liquefaction.
_Fadul (1977) recently completed several years of soil study in the Atbara-Nile area of the Sudan. Demonstrating that the current theories about the formation of the vast Sudan plains are untenable, he has built up a convincing case for the deposition of soil materials by catastrophic mudflows extending over many thousands of sq. kms. The evidence for past mass movements in many level areas in different continents suggest that they are also responsible for many sediments....
[COVERSANDS]
_In western Germany, E. Holland and N. Belgium, the so-called Coversands are spread out over large areas. The present relief consists of smooth ridges and mounds separated by level areas that are between 1 and 5 meters lower. The age of deposition of the Coversands is generally thought to be Late Pleistocene to Early Holocene (about 10,000 years B.P.).
_the mineralogical composition shows a clear differentiation into three groups from north to south; the boundaries between these groups are oriented east-west (Crommelin, p. 144).
_Lumps of silt embedded in sand and the presence of stones give together a polymodal character to the sediment. This is difficult to explain by alluvial or aeolian processes, but it is typical for sediments originating from mass movements (see e.g. Blatt e.a., 1972, and Sharpe, 1960).
_Sharply angular stones [are] frequently found in the Coversands. ... It is impossible to reconcile [this fact] with alluvial or aeolian processes. Therefore I forward the hypothesis that the Coversands were transported in the form of mudflows, at different periods. The direction of flow was most likely from east to west.
_Combining facts and plausible hypotheses, I reach the tentative conclusion that most of the ridges are remnants of an earlier, more level deposit, and that most of the intermediate lower areas, including many wide flat valleys, are the scars of subsequent degradational processes. To explain the formation of wide flat valleys in the Coversand area, an analogy with the estero formation described in an earlier paper (Goosen, 1972) is drawn. These esteros are shallow, wide and flat-bottomed valleys developed in the level Orinoco plains of eastern Colombia. I have forwarded the hypothesis that they were formed through successive liquefaction and soil flow that sculptured them out of the land. Both the soil properties with regard to susceptibility to liquefaction and the general topography are similar in the Colombian Llanos and in the Coversand area of the Netherlands. The relief is somewhat more pronounced in the Netherlands, but the difference is not fundamental. Within a generally level area of soil materials susceptible to liquefaction, zones with better drainage will suffer less from liquefaction than zones with poorer drainage, as abundance of water is indispensable for liquefaction. If wide flat valleys were scoured out in successive steps by liquefaction and flow, then its higher-lying borders would become better drained. The subsequent development of a nearby valley will then not penetrate to the better drained borders of the earlier valley, but will follow a retrogressive direction more or less parallel to the earlier valley.
_Firstly, with the land sloping from east to west, many valleys are wider in the upstream than in the downstream part.
_Secondly, it appears that several valleys are discontinuous.
_Regional liquefaction and flow of surface soil must have had a tremendous impact on agriculture. When the upper horizons are sheared off through liquefaction, the natural vegetation would be destroyed and the exposed subsoil would be much less fertile for a number of years. There are several historical descriptions fitting this picture.

Horizontal Landslides During the 1960 Chile Earthquake [Catastrophism Geology] Year 1 No. 2 (Dec 1976)
_The 1960 Chile earthquake has had great repercussions, not only because of its magnitude and of the havock it has wrought, but also because of the lessons it has taught us about the possible role of earthquakes in geomorphology and in tectonics: landslides can move over considerable horizontal distances, whole provinces may suffer sudden elevation or subsidence, and we shall have to take into account the possibility that alpine nappes can be formed in a matter of minutes only. Also, the role of turbidity currents in shaping the circum-continental relief may have been much overrated.
_The magnitude of the heaviest of a series of shocks that devastated Chile on May 22, 1960, was calculated at Strasbourg (J. Rothé, personal communication) at between 8.5 and 8.6, and is therefore one of the most violent shocks known.
_The main effects of the earthquake may be classed in 4 different categories: Partial or total destruction of buildings, roads, railways and harbour facilities, caused by the seismic shock proper. Destruction, mostly total, caused by the tsunami. Subsidence of a coastal strip several hundred kilometers long and probably tens of kilometers wide. ... The total surface lost through inundation is estimated at 600 sq. kms.
_In the face of such overwhelming evidence for horizontal displacements, we are entitled within reasonable limits to make several extrapolations. The conditions prevailing in this piedmont region of the Cordillera were not at all favourable to great mass movements: the distance from the epicentre was more than 200km, the ground was dry, and the surfaces over which the avalanches moved were horizontal. In spite of this, considerable masses were transported to places up to 1 km from their point of origin.
[SEAFLOOR RIPPLES]
_sediment transport in the sea requires an explanation, and Oulianoff considered a mechanism identical to the one ... for the horizontal translations observed in Chile: a vibrating pathway moved by the Earth's seismicity. He brought a new argument in support of his hypothesis - that of the presence on the ocean floor of giant ripple marks. Jacques Picard, the first to descend, with the bathyscaph Trieste, into the oceanic deeps, has taken photos at 2800 metres, of ripples measuring two metres from crest to crest and half a meter deep. These are conventionally explained by wave-, surf - or stream-action. But no wave or surf can exert any influence beyond a depth of 200 metres....
[ALPINE NAPPES]
_An even greater mystery are the alpine nappes, these folds so exaggerately overturned and so stretched out that their lithified layers have become transported scores of kilometers from their original location. Next to the conventional hypotheses of compression and of gravity flow ..., we are led to consider henceforeward the possibility that they were formed during world quakes. ... The importance of earthquakes as an agency in geomorphology, sedimentology and tectonics now seems established beyond reasonable doubt, and it would be interesting to examine a host of unexplained features of land forms, sediments and fold mountains in the light of the lessons taught by the Chile earthquake.