LONG SUBMARINE LAVA FLOWS - OBSERVATIONS AND RESULTS FROM NUMERICAL MODELING

Long (>100 km) lava flows are relatively common on Mars and Venus and have been identified on the Moon, but they are rarely documented on Ea rth. However, although similar to 75% of the Earth's surface is covere d by water, only a small percentage of the ocean floor has been invest igated at a resolution sufficient to unequivocally identify the bounda ries of long submarine lava flows. Even so, basaltic lava flows as lon g as 110 km have been identified on the deep (>1500 m) seafloor near H awaii and the East Pacific Rise. Ambient conditions on the deep ocean floor may favor the development of long lava flows for the following r easons. First, high pressures (>15 MPa) keep volatiles dissolved in ba saltic lavas, preventing viscosity increases associated with exsolutio n and vesiculation. Second, seawater rapidly quenches the surface of s ubmarine basalt flows so that an insulating glass layer, 1-5 cm thick, encases submarine flows within seconds after their emplacement. This glass rind effectively insulates the molten flow interior from additio nal heat loss, making submarine basalt flows behave as well-insulated, subaerial tube-fed flows. Thus, for identical basalt flows emplaced o n the deep seafloor and subaerially, a submarine flow could advance fa rther before stopping. Results of numerical modeling indicate that thi n (less than or equal to 1 m) submarine basalt flows behave similarly to identical subaerial flows, but thicker submarine flows may advance significantly farther than their subaerial counterparts.