The aim of this paper is to present a summary of current knowledge about Quaternary climatic changes, sea level fluctuations, tectonic deformation, and volcanic activity in Chile. In the Andean highlands of the hyperarid desert, glaciers and lakes fluctuated repeatedly. Evidence of pluvial periods is not well documented in the marginal desert. On the contrary, pronounced climatic changes are recorded in semiarid Chile. In central Chile two or three major glacial advances have been identified, but they remained confined within the high Cordillera. In the longitudinal valley of the Lake Region geomorphic remnants of four glaciations have been described;14C dates are available for the last glaciation. The glacial history of the Fjord Region is still obscure. Whether Pleistocene climatic changes in the northern and southern part of Chile were synchronous or not is a problem which requires further investigation. Sea level fluctuations along the Chilean coast are in part ascribed to glacio-eustatic effects. They left striking sets of step-like marine terraces in northern and central Chile. From a paleontologic point of view the Pleistocene corresponds to a pronounced move toward isolation and endemic development of the marine fauna. The Quaternary tectonic tendency seems to be toward extension and not compression expected as sea-floor spreading compensation. Normal faults limiting uplifted, downwarped, and tilted blocks are common. Folds are rarely found. Northern Chile is characterized by an imposing chain of about 600 stratovolcanoes. They rest on Tertiary ignimbrites which cover thealtiplano. Quartz-bearing latite-andesites are predominant. Present volcanic activity is sporadic and weak. South of a conspicuous gap between 27 and 33°S, Quaternary volcanism reappears in the high Cordillera, and many volcanoes have erupted violently within historic times. Rocks are fundamentally andesite or basaltic andesite. Poorly sorted ashes including pumice clasts in the Central Valley south of Santiago are interpreted as volcanic mudflows of late Pleistocene age.

The Medjerda deltaic plain corresponds to a former marine gulf which has been progressively filled up during the Holocene up to the historic period as a result of numerous shifts of the river course. The area is relatively well known from archaeological viewpoint since ancient writings, relating events which took place here in Antiquity, are available. Many scientists - historians, archaeologists, geologists, geomorphologists, hydrologists - have been for a long time interested in unravelling différents stages in the development of the deltaic plain. As soon as 1884, Ch. Tissot suggested that the deltaic plain developed from south to north in historical times. Such proposal is still considered as valid. The crucial point is to determine when the Medjerda river shifted northward, opening a new channel between the former Utica peninsula and the Galaat el Andless promontory (Castra Corneliana). As a result, the harbour of Utica filled up and the city declined. During a recent archaeological and geomorphological survey covering the entire deltaic plain, ceramics were collected from fifty sites and dated. They point to an early filling up of the former gulf, especially of the area south-east of Utica. Therefore investigations aimed to find out remnants of the ancient harbour facilities have to be carried out on the northern side of the peninsula. Pre-roman settements existed on the clay dunes scattered in the surroundings of Pont-de-Bizerte. Such an early human occupation suggess that the central part of the deltaic plain dad been already filled up prior to the foundation of Utica when the so-called Chaouat channel, whose traces are still visible north of Jebel Maiana, was operating.

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The extension of the Quaternary glaciations has been studied in the semi-arid Andes of north-central Chile, where the glacial modelling is striking. In the Elqui valley (lat. 30°S.), two glacial advances were identified reaching down to 3 100 m (Laguna glaciation) and 2 500 m (Tapado glaciation). In the Aconcagua valley (lat. 33°S.), moraines from three major glacial advances were found, at 2 800 m (Portillo glaciation), 1 600 m (Guardia Vieja glaciation) and 1 300 m (Salto del Soldado glaciation).The Quaternary glaciations were linked with a decrease of temperature, but more significantly with a marked increase of precipitation probably related to an equatorward shift of 5–6 degrees of the austral polar front. The results obtained in the semi-arid Chilean Andes are correlated with those recently reported from other sectors of the southern Andes.

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