Water rises at the vent at (or near) boiling and loses heat as it flows outward across the sinter apron, so temperature falls smoothly with distance from the center. Each extremophile species tolerates only a narrow temperature window, reflecting its own evolutionary adaptation, and each produces a distinct pigment for photosynthesis-related light harvesting or UV protection. Wherever the local temperature at a given radius falls inside a species' tolerance band, that species — and its color — occupies the ring at that radius. Raise the vent temperature and the whole gradient stretches outward, pushing every band further from center; lower it and the bands compress inward or vanish once their required temperature no longer occurs anywhere in the spring.
T(r) = Tambient + (Tvent − Tambient) · exp(−r / L)
L = decayLength / flowRate
band visible where Tmin ≤ T(r) ≤ Tmax
- Vent source temperature — the water temperature emerging at the very center; sets the hot end of the gradient.
- Runoff flow rate — faster flow carries heat further before it dissipates, stretching the whole gradient (and every band) outward; slower flow compresses it near the vent.
- Species bands — toggle the colored microbial mats on/off to see the bare thermal gradient underneath.
- Cross-section graph — plots temperature against distance from the vent, with each species' tolerance range shaded at the radius where it currently applies, so the color pattern above is a direct readout of the curve below.
Real-world relevance: this is exactly why Yellowstone's Grand Prismatic Spring shows deep blue at its scalding center and rainbow bands of orange, yellow and green radiating outward — each ring is a live map of a different thermophile community's temperature niche.