What foreshadows the massive volcano eruption?

Lottie stands looking across Spirit Lake. The ice on the lake has hairline cracks in it and Lottie wonders where spring is. As she starts her way back to the cabin, she feels tremors under her feet. She drops to her knees at the earthquake, but when it is over, nothing seems to have changed. Above her looms Mount St. Helens. A week later, the mountain blasts steam from its top and sulfurous gases spew out at random times.