We tend to think of disasters, like 9/11, as fixed in time. But they often ripple through communities. Photograph by Jim Watson / Getty

It sounded like an aluminum bat hitting a streetlight. Like a car crash. My uncle Ron Fletcher, a luthier, got up from a workbench at his home, in Lower Manhattan, and looked south out a window, down Lispenard Street. He saw smoke and called out to his wife, my aunt Marya Columbia, a violinist, who was in bed. It was just before nine on the morning of September 11, 2001. Together, they raced up to the roof. They watched the second plane hit, then the first tower fall. It looked as if the building sank into a pile of smoke, which fell low with it and then rose and spread across the sky. They went downstairs to turn on the TV and missed the second collapse. Later that morning, they were evacuated from their apartment, and, after they were allowed back in the evening (only after showing an I.D. that confirmed their address), they went for a walk. They’d seen people trudging past their apartment, covered with a fine, light-gray dust. That same dust coated the street, the ground. Ron remembers lifting up a handful of it and seeing scraps of paper—the size of quarters, burned at the edges—that looked like pieces of insurance policies and financial statements.

Marya, whom everyone calls Muffin (she didn’t know her real name until her first day of school, when a teacher called it out), was forty-five, with high cheekbones and eyes that shifted from green to blue to purple. She played a violin that Ron had found in a flea market, with a bow that he had made. When she was twenty-three, a cellist with the American Philharmonic overheard her practicing in her room through the window and invited her to audition. She landed a seat in the orchestra and played with the group for several years. An article in the Daily News called it “a New York fairy tale come true.” Later, she toured as principal second with the New York City Opera, and accompanied such musicians as Josh Groban and Diana Ross. In the days after 9/11, Marya watched a parade of rescue workers and volunteers pass through her neighborhood on their way to Ground Zero and had an urge to help. “I felt, like, What can I do?” she told me. “All I can do is play.”

Other musicians felt the same. A few days after 9/11, Marya got a call from a violinist named David Gold. He was organizing a string quartet to play in St. Paul’s Chapel, a block away from Ground Zero. The building, which is more than two hundred and fifty years old, is obscured by a half-dozen trees. One of the looming sycamores seems to have saved the chapel on 9/11 by absorbing debris from the towers. (The only damage was to the pipe organ, which inhaled so much dust that it had to be replaced eight years later.) During the months after the disaster, the chapel served as a kind of sanctuary. Firefighters, construction workers, police officers, and others would go there to rest, or for food, or to sleep on cots. Gold asked Marya if she would play for the first responders with him. “She’s got a huge heart—if you ask her to help someone, anyone, she’ll say yes,” he told me. “And, of course, the icing on the cake was that she lived in the neighborhood.” Marya agreed, and, for the next nine months, a large group of volunteers, known as the Music Givers, played three concerts a day at the chapel. (My aunt took the Monday-morning shift.) Mostly they played classical music, though, occasionally, they got requests for Billy Joel or the Irish ballad “Danny Boy.” “You know, we always felt, it’s so insignificant, what we do,” Marya told me. “But then we realized it is significant to these people to have a moment’s rest.”

It took days for the clouds of dust near Ground Zero to begin to clear. Ralph Farris, the volunteer coördinator for musicians performing at the chapel, could feel grit in his teeth on his way in and out. “I remember that really feeling so awful and strange,” he said. “I considered all the things I was ingesting. It was in my mouth. I was breathing it.” Gold told me that he remembers emerging from the subway and the smell hitting him—a mix of chemicals and burning metals that, in the early days, smelled almost sweet. “My reptilian brain was saying, ‘You should not be here at all.’ ” Gold said. “Every instinct in me told me, This is not a safe place to be.” None of the musicians I spoke to wore a mask.

Late last year, at age sixty-two, Marya got a cold that wouldn’t go away. When I called her to talk in February, her voice sounded hoarse. She went to the doctor, who took an X-ray of her lungs, found nothing unusual, and diagnosed her with high blood pressure. In May, she went back to the doctor, who took another blood pressure reading, and, finding it alarmingly high, sent her to the emergency room. A second X-ray revealed a tumor in her lungs. She was admitted to the hospital, where we later learned that the cancer had metastasized to her brain. An ache in her ribs that she thought was caused by a persistent cough was actually the splintering of bone, caused by tumors in her marrow. The cancer may have been related to toxins that she inhaled during her time at Ground Zero. The doctor gave us a timeline: “Anywhere from a few weeks to a few years.” Afterward, my aunt turned to the group of family members standing around her. “Looks like it’s curtains for the old girl,” she said.

We tend to think of disasters—and the impacts on the people involved—as fixed in time. In fact, disasters often ripple through communities, affecting people in surprising ways over decades. The victims of 9/11 have come in three waves. First, there were the immediate deaths and injuries caused by the towers’ collapse. In 2001, Congress created a fund to compensate those victims and their families, which closed in 2003. But, during the next several years, doctors noticed higher diagnosis rates of aerodigestive disorders related to the inhalation of particles released by the blast, including gastroesophageal reflux disorder and chronic rhinosinusitis, among survivors and first responders—the second wave. In 2010, Congress reinstituted the fund, this time with dispensation for volunteers and for New Yorkers who lived, worked, and went to school in Lower Manhattan. The World Trade Center Health Program (W.T.C.H.P.) covered health-care costs for eligible diseases, and the Victim Compensation Fund doled out payments for illness or death. The fund was due to run out in 2020, until activists (including, notably, Jon Stewart) pushed Congress to extend it by seventy years.

The last wave—which doctors believe could be about to swell—is expected to be comprised of people who contracted cancer from their time near Ground Zero. So far, the World Trade Center Health Program has documented an increased incidence of thyroid and prostate cancer among its patients. But lung cancers, which some doctors believe could pose a significant risk to people exposed to the carcinogens in the dust near Ground Zero, have a longer incubation period. Mesothelioma—a cancer caused by the inhalation of asbestos—can take thirty to forty years to manifest. Other lung cancers begin to appear around twenty years after an initial exposure. So far, six hundred and sixty-six patients at the W.T.C.H.P. have been diagnosed with lung cancer. But doctors at the program think that, in the coming decades, they may see an increase. “This is going to get worse,” Michael Crane, a doctor of occupational medicine who directs the W.T.C.H.P. at Mt. Sinai, told me recently. “A lot worse.”