- The slopes (left to right) are 15o, 20o, 25o, 30o and 35o.
- Soap bubbles show the flow at top and bottom of a trench.
- The trench measures 3 m x 60 cm.
- The disappearance of flow down the slope towards the flame for the two highest slopes shows that the air-flow becomes attached to the slope.
- The fires on these two highest slopes also demonstrate eruptive behaviour,
since their size and rate of spread increase continuously.
- The fires on the lower slopes all spread at a constant rate.
- A line fire is ignited at the base of a 23o slope in a plot of length about 40 metre on a mountain side in Portugal.
- There is a mild upslope wind and vegetation is typical Mediterranean schrub.
- A cloth tied to vegetation at mid-slope reveals attachment of the air-flow to the slope when the cloth blows up-slope.
- An eruption ensues.
- The spread-rate increases from about 6 cm/s before the eruption towards about 2 m/s at the top of the slope.