“Spontaneous shrines,” as Dr. Grider and other scholars describe them, beyond war memorials are a largely new phenomenon whose popularity can be traced to the 1997 death of Princess Diana. Ever since, and especially after Sept. 11, 2001, displays of affection and grief have become familiar elements of mass tragedy.

People left running shoes after the bombings at the Boston Marathon. A white supremacist’s massacre of nine black churchgoers in Charleston, S.C., led to more than 500 quilts, prayer shawls and other textiles. And in Orlando, Fla., where 49 people were killed last year at Pulse, a gay nightclub, there were 49 crosses.

“I don’t think you can possibly fathom the depth and breadth of a project that comes upon you so immediately in a crisis situation,” said Michael Perkins, who oversees curation efforts in Orlando and hired temporary workers to help with the deluge of items, only about 6,000 of which have been tallied so far.

“As much as the actual event can represent the worst of humanity,” Mr. Perkins said, “in many different ways, these memorials can represent the best.”

Not that good intentions make the task of people like Mr. Perkins any easier. Tributes are still arriving at Emanuel African Methodist Episcopal Church in Charleston, and more than two years after the attack, archivists are still grappling with issues of space and money. Yet they are preserving as much as they can; to do otherwise, they said, would risk history.

“These are materials that people created out of a sense of urgency and need, and it happens so quickly,” said Meg Moughan, the records manager for the City of Charleston and one of the people who has been involved with the preservation efforts. “You can’t really determine what it’s going to mean, but you know you have to take steps to keep these materials available.”

Preservationists say the written materials will prove most important to researchers. But as the collections await history’s judgment, and as the tragedies slowly fade from public view, the tributes remain poignant for family members and friends of the dead.