When Hillary Rodham Clinton disclosed that she had destroyed more than 30,000 emails about personal matters during her tenure as secretary of state, it was painful for historians and biographers. Some imagined themselves or their successors in 20 or 50 years prowling the archives with little success for the most intimate, revealing raw material.

The problem goes far beyond Clinton, though her private life as first lady and secretary of state — and, of course, if she were to become the 45th president — is likely to be of great interest to future generations. The advance of technology has created a huge volume of digital information, much of it ephemeral and easy to lose or destroy, while all but eliminating some of the richest sources for historians who have plumbed the 19th and 20th centuries.

The lost Clinton emails, said Doris Kearns Goodwin, might have helped fill in a vivid future portrait. "A government official is not just an official," said Goodwin, a Pulitzer Prize-winning biographer of Abraham Lincoln, Theodore and Franklin D. Roosevelt, and other figures. "They have marriages and children and rich private lives that are all mixed up with their public lives. As a biographer, that’s what you want."

At a news conference on Tuesday, Clinton emphasized that she had turned over to the State Department the 30,490 emails from her sole account that her staff judged to be work-related. But more than half of the emails she wrote or received from 2009 to 2013, about 31,830, she designated as personal in nature and deleted.

That would be more than 20 personal emails a day, on average, for the nearly four years that the account was operating, a period in which she traveled to 112 countries, oversaw U.S. diplomacy and burnished her status as one of the most famous women in the world. It was simultaneously a period of personal and family drama, including the wedding of her daughter, Chelsea, the death of her mother and a fall at her Washington home that left her with a concussion and double vision.

Her decision to delete the personal emails may reflect her experience as a polarizing figure who lived through the searing experience of her husband’s very public sexual affair with a White House intern. Now, as a likely presidential candidate, she opted to delete the private emails out of concern that they could leak and be used to embarrass her or undermine her candidacy.

"No one wants their personal emails made public, and I think most people understand that and respect that privacy," Clinton told reporters.

That may be. But historians, of course, perhaps after a grace period of some years, very much want to use personal emails and other private records to shed light on a public life.

"If she becomes president, we would eventually want to have all the intimate details of her life before the presidency," said Robert Dallek, a prominent presidential historian. "It’s all part of the historical record."

Dallek noted that many personal archives of public figures have been withheld from the public for many years after their deaths. But as long as the records are preserved, there is the possibility that they will someday add critically to the understanding of history.

For example, in the late 1990s, Dallek became the first scholar to be given access to President John F. Kennedy’s medical records, which were controlled by a panel of three Kennedy associates who had rebuffed researchers for decades after his assassination. The historian’s discovery that Kennedy had more serious health problems than previously known, and had been treated with an extensive arsenal of drugs, made news around the world.

"It provided a new perspective on his life and his presidency," said Dallek, who wrote about the records in his 2003 Kennedy biography.

While most government email is now subject to preservation rules, personal email can be deleted with a couple of clicks. While letters may have ended up in a shoe box in the attic, email accounts can be lost when users switch Internet providers. But for Goodwin, the problem goes deeper than the loss of such records. It is the nature of the technology, which she believes rarely provides the visceral intimacy of earlier records.

"What will be missing in the future is the best of the material we have today, which is handwritten letters and diaries," she said.

Several of Lincoln’s associates kept meticulous diaries that were crucial in writing her 2005 book on Lincoln, Goodwin said. For "The Bully Pulpit," her 2013 study of Theodore Roosevelt and William Howard Taft, their thousands of preserved letters, mixing family gossip and government business, gave an intimate, daily account of what they did and how they felt about it, she said.

"You feel like you’re looking over their shoulder as they write," Goodwin said. By comparison, she said, emails offer less depth and intimacy. "I would never write about a modern president," she said.

But for some historians, such complaints overlook the fact that technology gives as well as takes. There are hundreds of hours of video and audio recordings of a public figure like Clinton, in addition to recordings of her colleagues, friends and critics commenting on everything she did. She joined Twitter in 2013 to great fanfare, though her 132 posts to date are anything but revealing.

Some archivists, in fact, bemoan the overwhelming volume of material that this era will bequeath. Larry Cebula, a digital archivist for the state of Washington who teaches history at Eastern Washington University, apologized in a semi-serious blog post to historians of the next century for "all the stuff." If Thomas Jefferson were alive today, he wrote, he might be commenting on his friends’ Facebook pages and posting photos to Instagram.

"I think historians a century from now will view this period as a time of an explosion of records," Cebula said. "Even if Facebook is out of business, someone will have bought the archive."

Of course, politicians are naturally wary of some record-keeping. Clinton may have deleted half her emails, but her predecessor at the State Department, Condoleezza Rice, chose not to use email for work at all, partly out of concern that email mix-ups could lead to diplomatic or policy misunderstandings, her aides say.

A revealing precedent is the tape recorder. Kennedy’s selective taping left an invaluable record of White House discussions during the Cuban missile crisis, and Lyndon B. Johnson recorded fascinating phone calls with many contemporaries, including the Rev. Martin Luther King Jr. at the time of the civil rights marches in Selma, Alabama, 50 years ago.

But Richard M. Nixon’s tangle with taping, in which incriminating recordings during the Watergate scandal helped end his presidency, has left his successors disinclined to record.

"I doubt that we’ll find recordings from the recent presidents," Dallek said. "That’s a shame."

© 2015 The New York Times Company