An anomaly is a data point that does not fit the general pattern or trend of the rest of the data.
Explain two possible reasons for the anomaly shown at Z in Figure 1.

| Distance downstream from source (km) | Mean bedload particle size (cm) |
|---|---|
| 2 | 18 |
| 4 | 12 |
| 6 (Point Z) | 22 |
| 8 | 6 |
| 10 | 3 |