There are a few things that can cause bark splitting or cracking. Extreme heat or fluctuating temperatures followed by a frost event can cause sunburn and sunscald. Mechanical injury (e.g. the trunk was hit with a string trimmer) can cause cracks in the bark. Cankers caused by plant pathogens can sometimes resemble splitting or cracking in their early stages. Cracking due to fluctuating temperatures (e.g. sunny day followed by hard frost) or sun exposure in young trees is the most common cause. With sunscald and sunburn, the damage will usually appear on the south or southwest side of the tree. Apple trees, and fruit trees in general, are susceptible to frost cracking. For more information on sunscald and sunburn, refer to https://pubs.extension.wsu.edu/environmental-injury-sunscald-and-sunburn-on-trees-home-garden-series. In your case, the splitting does not seem too severe, and it is possible the tree will recover on its own. The main risk is that a wood boring insect or pathogen may enter where the tree has split opened. To prevent sunburn or sunscald, you can paint the trunks of young trees with a 50:50 mixture of white latex paint and water or place a white trunk guard around the trunk. However, now that the damage has occurred, it is best not to paint or cover it, since the paint or trunk guards can trap moisture causing decay. You can use a knife to try to trim away excess bark. This Cornell University factsheet provides a few tips on how to manage bark splitting: http://plantclinic.cornell.edu/factsheets/barksplitting.pdf

One other note, don't place wood chips right up against the trunk of the tree, they can trap moisture leading to rot or decay. Instead, place the woodchips like a donut around the trunk, with the woodchips 2-3 inches away from the trunk moving outwards.