One of the problems that parents face in trying to provide reinforcement and enrichment for the lessons their children learn in school is that some of those lessons deal with facts and theories that were not taught even a few years ago. So parents must keep an eye out for ways to refresh their own knowledge, and I try to make Family Learning a part of that process whenever possible by sketching out a useful area of study, and then providing information about low-cost and no-cost learning materials appropriate for use in the home.

I am reminded this week of a theory in geology called "plate tectonics" (tek-TAHN-iks), discussed only by scientists just a couple of decades ago and now taught in elementary schools and middle schools across the country. This theory comes to mind because it helps explain an event that happened just 11 years ago this week - May 18, 1980 - the eruption of the Oregon volcano known as Mount St. Helens.The volcanoes we studied in school were consigned, for the most part, to history classes, and, to be sure, there is a great deal of history to be learned from them. The eruption of Mt. Vesuvius (vuh-SOO-vee-us) in southern Italy in A.D. 79, for example, caught the people in the nearby city of Pompeii (pom-PAY) so much by surprise that many died where they stood, and the tons of ash and rock that covered the city preserved it for nearly 1,700 years, giving us our most accurate information about Roman life of that time.

And this Roman foundation to our knowledge of volcanoes was particularly important because there are so many things associated with volcanoes that have a Roman origin or connection. The word "volcano" itself derives from the Roman god Vulcan, who was the blacksmith for the gods and who labored at his forge deep inside a fiery mountain. The word "eruption" comes from the Latin word meaning "to break out or explode," and "crater" is the Latin word for "bowl."

We didn't think of volcanoes and earthquakes as being part of our time in history or our place on the planet. The Earth to us was truly solid ground, or in the Latin phrase, "terra firma." But today our children are learning that that ground is anything but solid, and volcanoes and earthquakes are just the most violent outcomes of the slow, constant and measurable drift of the Earth beneath our feet.

The theory of plate tectonics says that the surface of the Earth, its 50-mile-thick crust, is broken into several large, shifting slabs. Some of these slabs or plates bump into each other, some pull away from each other and some slide past each other. It is at the edges or boundaries of these plates, then, that molten rock from deep inside the Earth can find its way to the surface. The Earth is constantly reconstructing itself, and that is why the word "tectonics" applies. It pertains to "building or construction" and is derived from the Greek word for "carpenter."

The best visual display of plate tectonics I have seen is a large (58-by-41-foot) map of the Earth that plots all the major earthquakes and volcanic eruptions that have occurred throughout history. These marks on the map occur all along the various plate boundaries and form a stunning outline of the pieces in the Earth's fractured crust. The map, titled "This Dynamic Planet," costs $3 (plus $1 for handling) and is ideal for a classroom or bedroom wall. Send a check or money order to U.S. Geological Survey, Box 25286, Federal Center Bldg. 41, Denver, CO 80225. I suggest you request the flat (rather than folded) version of the map. There is also a free, 45-page pamphlet that the USGS has produced explaining volcanoes and plate tectonics, which can be obtained by calling 1-800-USA-MAPS and asking for the pamphlet titled "Volcanoes."- Dr. William F. Russell's books for parents and children include "Classic Myths to Read Aloud." Send your questions and comments about Family Learning to him at P.O. Box 1279, Menlo Park, CA 94026.