In which condition would well water typically contain more silica than surface waters?

In areas of high volcanic activity, well water is likely to contain more silica than surface waters due to the geological processes associated with volcanism. Volcanic rocks, such as rhyolite and basalt, are often rich in silicate minerals, which release silica when weathered. Groundwater can easily dissolve these minerals as it moves through volcanic rock formations, leading to higher concentrations of silica in well water compared to surface water sources that may be more influenced by soil and organic matter, both of which tend to dilute silica levels.

In contrast to volcanic areas, drought conditions do not inherently lead to increased silica levels in water. Drought may concentrate some minerals due to reduced water flow but does not specifically enhance silica levels. Similarly, low pollution areas do not provide a direct correlation to silica content since pollution typically affects chemical composition differently than geological origin. Cold weather regions may have less weathering and soil development, but they do not guarantee elevated silica concentrations in well water compared to surface water. Thus, volcanic activity is the strongest factor leading to increased silica in well water.