This tree snapped at the trunk, likely due to drought stress. Elms are very thirsty trees with a robust root structure and seek water wherever available. Positioned right next to a building on a slope, water is subject to runoff. In addition, the tree must compete with the lawn for water. They tree appears to have establish a stable root zone, not being uprooted. However, adequate water is necessary to keep trees strong and healthy. Lacking water, trees can become very brittle, yet may not appear so at a glance.