The laws of physics are immutable. In Newtonian mechanics, momentum is the product of an object’s mass and velocity. This could explain why Victor Abarzua—a man who is 6 feet, 5 inches tall and weighs 244 pounds—nearly leaves Ernesto “Máquina” Araneda in a puff of volcanic ash after straight-lining a 30-degree cinder cone on Volcán Batea Mahuida, a plateau-shaped volcano that straddles the border between Chile and Argentina.

When he was only 14, “Máquina” (Machine) was already a Chilean national mountain biking champion and went on to be a Pan-American Games bronze medalist and a World Cup Masters silver medalist. Now, he has young kids and works as a full-time guide, occasionally squeaking in an epic race when he can find the time.

Araneda has been quietly toying with me and Canadian photographer Kari Medig ever since we landed in his hometown of Temuco, a city located some 400 miles to the south of the Chilean capital, Santiago. We’d set off to explore a microcosm of frontier mountain biking in this land of lakes and volcanos, a place that seems naturally forged for vertical pursuits.

And here we are, ripping down an extinct volcano and trying to cling to the back tire of Abarzua—a former professional Chilean basketball player—as he carves high-velocity flow on a mix of sculpted singletrack and repurposed animal trails. For such a big man, Abarzua is remarkably agile. The descent culminates into a flock of noisy chickens free-ranging around a hamlet of wood-framed houses with tin roofs. It’s the village of Icalma, a community of mostly indigenous Pehuenche mountain people. Three men watch as we ride up, as though they’re expecting us. Turns out, they are expecting us.