When I recently met up with Robert Buchwaldt — a Boston University research professor — near the corner of Grove and Washington streets in West Roxbury, it didn't take long for him to teach me rule number one of geology.

"So as a geologist, you always have a hammer," said Buchwaldt, digging into the trunk of his car.

Within moments Buchwaldt was hammering away at an outcropping of rocks, just steps back from the sidewalk. To be fair, Buchwaldt was doing this because I asked him to. I mean, I didn’t know he was going to actually use a hammer, but I did invite him to join me here. I’d heard there was something special about this area of the city and hoped he could confirm whether it was true. And so, as he pried loose a rock sample for closer examination, I was on bated breath.

"You can see here, It’s a relatively boring rock," he explained.

But looks can be deceiving, especially when your companion can see the world in a way that you can’t.

"We can see there is a different kind of color of material sitting right in here," he said, pointing out maroon and purple colored flecks in the rock. For Buchwaldt, those tiny specks are a smoking gun. Or — perhaps more accurately — smoking hot, liquid magma.

"Roxbury — as quiet as it is today — around six hundred million years ago, this was an active volcanic scene," said Buchwald.

The rock Buchwaldt dislodged is rhyolite, and it sits here in this neighborhood like an island in a sea of granite. Granite and rhyolite are both made of the same molten hot stuff. But where granite cools slowly over thousand millions of years always just under the surface, rhyolite forms when that magma suddenly blast out into the open, and cools quickly over just weeks. Indeed, we are standing on a volcano.

As we traversed the ancient urban volcano, Buchwaldt explained that it's eruption would have had much more in common with Mt. Fuego’s recent sudden, violent bursting in Guatemala than the steady, ongoing molten hot oozing at Mt. Kilauea in Hawaii. I asked Buchwaldt to paint a picture of this landscape as it would have looked 600 million years ago.

"Bare rock," he said. "Like Iceland today. We had some moss. But trees, flowers, animals? All these different kinds of things are not existing at that time." It was an active subduction zone — like the American West today. Think fault lines, earthquakes, and active volcanoes. Oh, and mountains. Really. Big. Mountains.

"We are looking at a mountain range the size of the Himalayas...Right on top of us," said Buchwaldt.

And what happened to those mountains?

"They eroded," he said. "They got broken apart, over 400-600 million years, carried away into the Boston Basin, into the Atlantic, into the Gulf Coast. Some parts we probably can find in Africa."

Africa? You bet. Remember Pangaea from elementary school? Today’s seven continents have smashed together and broken apart multiple times over the course of Earth’s more than four billion years.

"It’s not one big fragment of continent but it’s broken apart, welded together again, broken apart, welded together again," said Buchwaldt.

Case in point: While the bedrock that comprises most of Massachusetts is as old as the granite and rhyolite here in West Roxbury, the eastern-most puzzle piece? Cape Cod? That land was carried here by glaciers and deposited as a new coastline just 10,000 years ago.

"As geologists, we’re trying to figure out — every day — what is the meaning of that puzzle," said Buchwaldt.

And so, hammer always in hand, Buchwaldt will continue to dig for the stories hidden in the ancient rock beneath our feet.

"It's my passion," he said. "It’s important to understand how our landscape was actually formed. Today we have to think [things as] not only just geology, or just biology, but as an earth system...everything is interconnected."

Oh, and one more thing. You might be wondering if this volcano here could erupt again? Buchwald says, not a chance. At least not in our lifetimes. Still, a new study released just this week shows there’s a huge mass of molten rock slowly welling up deep beneath New England. Will it ever surface? As the study’s co-author said, “come back in 50 million years and we’ll see what happens.”

We're always looking for story ideas here at the Curiosity Desk, and the best ones often come from you. What have you been curious about lately? Email me at curiositydesk@wgbh.org and let me know. I might just look into it for you.

