In time, eastern Africa will break off and float away, and the rest of Africa will shimmy northward, closing off the Mediterranean and bumping into Europe. Meanwhile, Los Angeles drifts toward Alaska at the rate of two to three inches per year, which can't be good news for the maitre d' at Ma Maison.

Such geological bulletins do not strike with much urgency as related on "Born of Fire," the latest National Geographic Society Special, at 8 tonight on Channel 26. Although one may be prepared to accept the program's definition of the earth as "a very dynamic object, a living organism," the documentary is not nearly so compelling as Geographic specials about pandas and sharks and golden toads.

True, various parts of the planet are always on the verge of erupting, and it is worth considering whether man will be able to wipe himself off earth's face before earth itself manages to do it (born of fire, die of fire?). But the program's footage of volcanos and schisms and rock formations lacks oomph, and Robert Ballard, the geologist featured prominently, seems to be auditioning for the part of the next Carl Sagan, and not too convincingly.

Among the locations visited during the hour are Santorin, an island in the Aegean; Iceland, where volcanic splooshes are extremely photogenic; and cities along or near the San Andreas Fault in California, like San Francisco, where "it's just a matter of time," Ballard declares, until there is another quake even worse than the one in 1906. That is, Spencer Tracy, Jeanette MacDonald and Clark Gable might not make it through this time.

The script by Theodore Strauss is marred by a dry triteness, or by such quantum reaches as linking Easter with deliverance from earthquakes in a village where, says narrator E.G. Marshall, "faith holds a triumphant hope." This Geographic special seems not only fitfully softhearted, but occasionally softheaded as well.