_{Photograph: Riots on the streets of Tottenham (detail) cc Nico Hogg}

"SO WHAT'S GOING ON with those London riots, then?" asked the cab driver. I was headed to JFK en route to Heathrow; after eight years living in the U.S., I was returning to the U.K. He told me what he'd heard from the BBC, Fox News, Sky, and I chipped in my two cents, thinking back to when I was last living in North London, sharing what friends still living in the capital had told me.

I'd spent the day before listening to two soundtracks: first, the raised yells, splintered glass, dull thump of heaved bricks as another plate glass window in another high street shop, someone's livelihood, someone else's nine-to-five, shattered. The videos on the BBC website, some still live, brought the third night of riots in London, Birmingham, and Manchester into my home in three-by-five inch frames. Buildings the size of traffic circles shot flames 15 feet into the air.

Commentators on newspaper blogs and Facebook reported the latest, sounding their alarm, calling out these yobs, this riffraff, these kids. Some politicians were already blaming social media for stoking the riots. Meanwhile, local residents used Twitter to find one another and begin the clean-up. #whatjusthappened

I watched bands of hooded looters range the streets, jubilant, fired-up; some passersby nervously turnedthe other way, some paused to get out their camera phones. I was here when...What does it mean to be present for these riots, which for me take place in a London that used to be home, in a U.K. where I'm about to, as they say, repatriate? How can any of us make our presence at these riots meaningful, admit our implication in them?

The second soundtrack to my morning had no answers but some useful puzzles. The graveled voice of the new American poet laureate, Philip Levine, recited his poem "They Feed They Lion." Written in the late nineteen-sixties, about the 1967 Detroit riots, where 43 people were killed, 470-odd injured, over 2,000 buildings destroyed, this poem disturbed my morning in the present, as it should:

Out of burlap sacks, out of bearing butter,
Out of black bean and wet slate bread,
Out of the acids of rage, the candor of tar,
Out of creosote, gasoline, drive shafts, wooden dollies
They Lion grow.

The poem, written out of an experience of working in grease shops, is not an explanation for the riots. It's like a transcript of the city's industrialized energy, all camshafts and nightshifts. In Levine's poem, something emerges from where it has been waiting, lingering. While he lists the hackneyed causes of riots - new migrants, impoverished urban estates, white privilege - these heaped "out of" phrases collide with one another to complicate our ability to say: this is how and why it started. "The acids of rage" won't place the blame on a single ethnic, economic, or geographic group nor, as the U.K. Justice Minister Kenneth Clarke has done, on that old fallback of "a broken penal system." Instead, this poem makes us think hard about industrialization and community, about "gasoline" and "the bones' needs to sharpen and the muscles' to stretch."

"They lion grow," that beautiful, terrible refrain, originates in a self-conscious black vernacular: it comes from a sentence spoken by a...