The black line shows water in the functioning canal bypassing the flood-prone valley. All the sections are part of the 1, km2 Valensole Tertiary molasse depo basin sedimentary sequences that were eroded from developing mountain chains. The basin received sediments eroded by rivers from the southern Pre-Alps. The present morphology reflects the subsequent dissection of these weak sediments.
The linearity of the Durance is controlled by a major regional fault. The braided channel Fig. All green areas are woodlands. The poor permeabilty of such fine-grained clastics results in minimum rainfall infiltration, and erosion by development of surface runoff closely spaced drainage systems. Geohazard relations Hazards associated with shales are essentially related to their low resistance to mechanical weathering and erosion.
Their variable strength is related largely to their water content.
They are susceptible to sliding and slumping and generally provide poor subgrade support for structures due to high compaction potential. The characteristic surface runoff erosion of the shales contrasts strongly with the fractured terrain of the gneisses. Close examination of the south contact suggested that it may be faulted. Four rock slides Fig.
A debris slide Fig. The image area is at the southern margin of the km long crystalline Pelvoux massif of the French Alps. The red line marks the contact between the Precambrian massif and Upper Eocene folded and thrusted shaly sediments which are indistinguishable morphologically from the crystalline rocks. This situation is explained by Verstappen in Fig.
Rust colored highlands are above timberline; blue is snow at over 3, m elevations. The river in the photo is the upper source of the braided Fig. They result from disruptions in the depositional process. The resistant strata are in ledge outcrops over or between the recessive argillaceous beds. They commonly show banding on aerial photographs. The banding will coincide with the contours of the land surface. Geohazard relations The main geohazard associated with these rock sequences is the risk of landslides Fig.
Figures 35, 36 and 37 of the Geostructures Section show and explain how the identification of dips and strikes of such exposed strata are the basis of mapping deformed Geounits. These are arrayed in roughly two kilometer wide segments from southwest to northeast. The contact between Types 2 and 3 rock units is marked by a prominent linear m high scarp which is interpreted as a probable fault trace Fig.
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Types 1 and 2 are parts of two obliterating open anticlines Fig. The area is in the southern sector of the intermontane Altiplano basin of the central Andes. The bright area in the scene center is an extension of Type 3 in the Fig. Figure 28 Interbedded sedimentary rocks class. W1 Characterization see Figure 27 Fig.go here
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The area is fluvially dissected in narrow valleys with steep slopes. The dark scrub-covered beds are the sandstones. The strata at the northeast edge of the photo are dipping south, the rest of the beds are near- horizontal. The interbedding is most evident in the agricultural west half of the photo.
The east half is in oak forests. The bright dissection of the marls can be seen on the left. One of the units contains hydrocarbons and sedimentary uranium deposits Fig. The sedimentary belt is km long. This area was deglaciated 9, years ago. In contrast to intrusive magmas metamorphic rocks are foliated or massive but contain no strong joint systems Fig. R1 Characterization These Units are belts of orogenically metamorphosed sedimentary or volcanic rocks that show compositional banding or planar structures e.
The laminated structure results from the flattening of the constituent grains of a rock. There are no strong joint systems. In areas of metasediments airphotos indicate bedding rather than foliation. Delineation on the stereo mate included in the extra material on the Springer website of this pair identifies four structurally-associated Geounits: Unit 1 are the foliated schists; Unit 2 are unfoliated younger weaker sedimentary rocks these appear as a light grey band in the northwest of the printed photo ; Unit 3 are foliated gneisses; Unit 4 are weakly foliated possible migmatites rocks that are transitional between granites and crystalline schists.
The band of coarser-grained gneisses of Unit 3 has definite but imperfect foliation compared to the schists. The four photo units are also distinguishable in the image. R2 Characterization Rock Units of low level metamorphism such as quartzite, hornfels or marble, are composed of randomly oriented minerals that give the unit a lack of banding, i. The morphologic and tonality contrasts distinguish three classes of Lower Precambrian metamorphic rocks.
R1 foliated gneiss, R1 unfoliated schist, and R2 non-foliated quartzites. The dark schist area is in an upland trough about m lower in the center of the belt which is at about m elevation here. The relatively featureless area in the northwest quadrant is part of the Volta Basin of interbedded Fig.
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A prominent strike-slip fault Fig. Section 3 Metamorphic Rocks 97 Figure 32 glaciated cratonic foliated rocks class. Minor structural features may stand out in relief. Figure 33 non-cratonic massive rocks class. J2 Fig. The western half of the area is in gneisses and migmatites Fig. The terrain on the east is later Mid Proterozoic plutonic granites Figs. The characteristic relief of the Units is visible monoscopically in this region. The only occurrences of surficial deposits detected in the stereo model are a small 15 km2 zone of shallow, eroded glacial till labeled Gf3.
The western half of the scene clearly displays the contrasting foliated metamorphic rocks of the photo area and the granite terrain on the east. A stock-like Fig. The northeast corner of the scene touches Fig. Characterization With the exception of their tectonic setting the rocks of this Unit are similar to Fig.
Relief range is from to m. The cleared areas are rough pastures. The arcuate white line in the center of the photo area is a fire break cut along a ridge line. The surfaces cut across, and are essentially devoid of control by, underlying metamorphic structures. This is an uplifted Eocene peneplane surface cut across Cambrian gneisses. A thin cover of surficial deposits conceals the bedrock see Berger quote in discussion of Geostructures. The beach is in a bay at the mouth of a depression of weak Carboniferous schists.
The intense local land use pattern is characterized by the French bocage system of field enclosure by thick hedgerows. The peninsula is composed of the gneisses of the photo area on the north and Ordovician granites of pointe du Raz on the south. The two areas are separated by the dark linear band of a two kilometer wide regional fault-associated depression eroded in Carboniferous schists and occupied by dense, hedged, horticultural land use. The general rectilinear shape of the peninsula is controlled by faults on both north and south coasts.
Part II The Examples Section 4 Geostructures Geostructures are bedrock Geounits that have been deformed or displaced by folding, faulting, or igneous intrusion processes. Berger Figures 42, 43, and 44 are examples of known faults. They include linear arrangements of natural geomorphic or radiometric features marking fracture traces Fig.
Photogeologically the stereo expression of dipping rocks is exaggerated. This property is helpful in structural interpretation but caution must be exercised because of the exaggeration. For example the moderately dipping beds in Fig.
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The ridge crest is at elevation. The small town of Poopo is on a fan at the mouth of a creek at the north end of the Unit. The line at M indicates a possible thrust fault Fig. The 35 km long red delineated zone contains a number of morphologically anomalous Units that are associated with the economically important belt of polymetallic vein deposits of southwest Bolivia. Two mines large enough to resolve in the 30 m image are circled. The northern mine, a tin producer, is at Morococala; the southern mine, another tin producer is at Catavi.
They are both located in relatively undeformed rocks. The deposits are intimately related to intrusive rocks in a variety of host rocks.