Two Stone Spirals in the School Scent Garden

The Scent Garden Report

Two low stone spirals curve around lavender and thyme in a school scent garden. Students call them the east spiral and the west spiral. The stones have similar sizes and are the same kind of rock. After a rainstorm, students saw water rushing through a gap in the east spiral. A new groove crossed the soil below the gap. Muddy water flowed out of that groove. At the west spiral, water spread across a wider area, and the students saw no new groove.

On a dry afternoon, loose grains lifted from soil beside the east spiral and landed on a nearby mat. The teacher photographed the moving grains. During winter, the teacher also photographed two similar stone cracks. Water often collected in the east crack, which widened from 1 millimeter to 4 millimeters after several freezing and thawing periods. The sheltered west crack stayed dry and remained 1 millimeter wide. Water takes up more space when it freezes.

In spring, students tracked two other cracks. A root inside one crack grew thicker. That crack widened from 2 millimeters to 5 millimeters. A nearby crack without a root remained 2 millimeters wide. The students left the roots and stones undisturbed. Weathering means rock breaks into smaller pieces. Erosion means loose rock or soil moves from one place to another. A place can show evidence of both changes at different times.

To investigate flowing water, the class made two matching soil channels. Each tray held 600 grams of the same soil, packed in the same way. Tray size, slope, channel shape, and starting soil dampness matched. Students poured 300 milliliters of water from the same height into each channel. One pour took 60 seconds; the other took 20 seconds. They collected the soil that washed out, dried it, and measured its mass. The graph shows their results.