Keeping your log cabin home warm and insulated requires regular maintenance. Your maintenance plan should include closing gaps in log courses. The two methods that are primarily used to repair gaping log walls are chink and caulk. Caulk is typically used when the gap is ¾ of an inch and chink is used when the gaps are larger. Both chink and caulk are designed to withstand the normal movement and settling of the cabin.
Modern chinking materials are more flexible than older cement based materials and are less likely to loosen over time. When done properly, chinking will last several decades. Proper chinking 
requires the use of a backing rod to provide joint insulation.
This reduces the amount of chinking needed. The goal of the backer rod is to provide a two point adhesion to the wood above and below the chink. It also prevents the chinking from experiencing too much stress. If a backing rod cannot be used because the gap is too shallow, caulk is generally a better solution.
Caulks are soft waterproof compounds that do not breathe. Caulks are not designed to be flexible. If the area is experiencing significant movement, a sealant is a better solution. The elasticity helps maintain joint integrity.
Make sure you know how to repair gaping log walls in your cabin!