3. A minimal volume of 5 ml of a pooled BAL sample is needed for BAL cellular analysis. The optimal volume is 10 to 20 ml. It is acceptable to pool all aliquots of the retrieved BAL ï¬uid for routine analyses (including the ï¬rst retrieved aliquot). 4. BAL cell differential counts with greater than 15% lym-
So when a continent meets a continent, no subduction occurs (instead, the plates collide and thicken). True subduction happens only to oceanic lithosphere. When oceanic lithosphere meets continental lithosphere, the continent always stays on top while the oceanic plate subducts.
1 First, in most subduction zones, large earthquakes occur at the interface between the two plates, at depths ranging from the earth's surface down to about 600 km. 2  This region, called the Benioff Zone , is used to locate the subducting plate, as shown for the case of Japan on the left-hand side of Figure 2. Second, in most subduction zones, there is an inland volcanic arc running parallel to the trench. 2  But in southern Mexico, the volcanic arc bends away from the trench, at about a 15Â° angle (see Figure 1). 3  Finally, in most subduction zones, giant earthquakes occur every few hundred years or so.