3 LONG LAVA FLOWS IN NORTH QUEENSLAND

The Kinrara, Toomba, and Undara basaltic lava flows are from 55 to 160 km long and range in age from 13 to 190 ka. The lavas were emplaced d own low gradients (0.2 degrees to 0.4 degrees) with volumes ranging up to 30 km(3). They were not unusually hot at eruption (1130 degrees-11 60 degrees) nor unusually fluid. Gentle topography controlled the Rows , and shallow drainage lines captured them. Lava tubes operated in pla ces, and some drained to form caves. Injection under surface crust was widespread, producing inflation features ranging from tumuli and low plateaus to extensive ridges. Sustained eruption was essential for the development of the long flows, but each is composite, with pauses bet ween successive pulses that partially covered the earlier, longer flow s. The lava structures are mainly pahoehoe but some 'a'a lavas are pre sent. Of the three volcanoes involved, Undara is a simple low-angle la va cone with a 200-m-wide crater, Toomba is a low-angled cone with sev eral eruption centers, and Kinrara has a deep crater with evidence of strong fountaining. Effusion rates are not known but may have been rel atively low, similar to those observed in Hawaiian volcanoes. Lava tub es, most of which remained undrained, are believed to have been of maj or importance in flow emplacement. Given the evidence of successive fl ows and the time needed to develop widespread inflation, it is suggest ed that the two long flows over 100 km involved many decades of erupti on.