Some people may presume that the archives hold an entire view of history; however, that is often not the case. Archival silences occur when the lives and voices of marginalized groups have been excluded from the archival record, either purposefully or due to a lack of material culture.
As an example, SCU Archives & Special Collections has a collection of materials from Mission Santa Clara. Included in this collection are baptismal and death records, library books from the Franciscans, and a "how-to" book that describes medicinal remedies, recipes using local plants, etc. Missing from this collection are things that represent the Ohlone experience at Mission Santa Clara from the viewpoint of the Ohlone. While we have descriptions of the Ohlone from the Franciscans, we do not have a description of life for the Ohlone from a member of the Ohlone tribe. This may be because (a) archives, including our own, prioritize the study and preservation of history through the written word, which is a worldview different than many indigenous North American cultures; and (b) those in power at the time did not feel that the Ohlone viewpoint was worth preserving.
The following video (8:23) from TEDxPittsburgh features Dominique Luster, the Teenie Harris Archivist at the Carnegie Museum of Art, and describes how archival representation is important in preserving a community's culture.
Archives are places of power. Archivists have the power to decide what historical artifacts are retained and what are thrown away or not collected. In doing so, archivists shape collective memory. By examining archival silences, students can critically question the history they are being presented with and determine who's story is not being told. In doing so, they gain a fuller picture of history. They can bring to light the structural inequalities that were in place during certain points in time (and now), and explore why those inequalities existed. The archive may show only one side of the coin--students should determine what that side is, and what side is missing.
If you're interested in learning more about archival silences, why they exist, how they can harm marginalized communities, and how communities can actively choose silence as a means of controlling their own narrative, I recommend the following articles: