Abstract Preserved rocks in the Jurassic Ferrar Large Igneous Province consist mainly of intrusions, and extrusive rocks, the topic of this chapter, comprise the remaining small component. They crop out in a limited number of areas in the Transantarctic Mountains and southeastern Australia. They consist of thick sequences of lavas and sporadic occurrences of volcaniclastic rocks. The latter occur mainly beneath the lavas and represent the initial eruptive activity, but also are present within the lava sequence. The majority are basaltic phreatomagmatic deposits and in at least two locations form immense phreatocauldrons filled with structureless tuff breccias and lapilli tuffs with thicknesses of as much as 400 m. Stratified sequences of tuff breccias, lapilli tuffs and tuffs are up to 200 m thick. Thin tuff beds are sparsely distributed in the lava sequences. Lava successions are mainly 400–500 m thick, and comprise individual lavas ranging from 1 to 230 m thick, although most are in the range of 10–100 m. Well-defined colonnade and entablature are seldom displayed. Lava sequences were confined topographically and locally ponded. Water played a prominent role in eruptive activity, as exhibited by phreatomagmatism, hyaloclastites, pillow lava and quenching of lavas. Vents for lavas have yet to be identified.

Abstract Repeated small eruptions of basaltic to intermediate magma produce monogenetic volcanic fields, which are common worldwide. The variety of volcanic landforms produced in such fields is controlled by whether or not water is present at or near the surface at the time of eruption. Basinal settings are typically "wetter," and hydrovolcanic eruptions produce tuff cones, maars and tuff rings instead of the scoria cone fields developed in dry, upland settings. Hydrovolcanic fields produce less lava and relatively more clastic debris than scoria cone fields and often contain large craters excavated by maar eruptions. Tephra eroded from volcanoes within hydrovolcanic fields tends to be reworked and redistributed within the basin in sheetform deposits and as crater-filling sequences, whereas the tephra eroded from scoria cone fields is largely carried from the fields in deeply incised streams skirting the fields' lava flows. The stratigraphic records of both groups of monogenetic fields differ from that of large, long-lived polygenetic volcanoes: the record of monogenetic volcanism is chiefly the result of long periods of inter-eruption erosion and sedimentation, whereas that of larger volcanoes is typically dominated by rapidly deposited units produced in immediate response to large eruptions.