Why does water in geysers not boil at the normal boiling point of 100 °C?

Water in geysers does not boil at the normal boiling point of 100 °C due to the high pressure exerted on it by the overlying water and geological formations. As water is heated in the Earth's crust, it experiences increased pressure, which raises its boiling point. This means the water can remain in a liquid state even at temperatures well above 100 °C, allowing it to accumulate until the pressure is released suddenly, resulting in a geyser eruption.

The other choices do not accurately address the reason behind the behavior of water in geysers. For instance, while recycling is a characteristic of water in these systems, it does not directly impact the boiling point in the same way that pressure does. Similarly, the temperature of surrounding rocks can influence the heat but does not determine the boiling point of water under pressure. Lastly, the presence or absence of oxygen in the underground chambers is not a factor that affects the boiling point of water; instead, it more closely relates to the oxidation state and reactions, which are not relevant in this context.