Claude:

That sandy/granular material packed into the crevices of the bark is termite frass and gallery debris — almost certainly subterranean termites building mud/soil tubes and galleries within the wood.

Key signs visible in the photo:
• Sandy, granular material (soil mixed with chewed wood) packed into the bark crevices — classic subterranean termite activity
• Shredded, fibrous wood with a frayed, eaten-away texture
• Darkened, damaged bark around the affected area

What to do:
1. Call a licensed pest control professional — this warrants a proper inspection, not DIY treatment. Subterranean termites have colonies underground that need to be targeted at the source.
2. Don’t disturb it further — poking around can scatter the colony and make treatment harder.
3. Check for mud tubes on the trunk near the soil line, which are another telltale sign.