大约30亿年前，洪水形成了流出通道，大约与北部火山平原形成的时间相同。

Flooding shaped the outflow channels approximately 3 billion years ago, about the same times as the northern volcanic plains formed.

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这些活动同时作用，形成火山平原，这是一个火山活动影响地质构造的重要标志。

Together these deposits create a surface feature shaped like a volcanic shield – a clear sign to scientists that volcanic activity helped form the surrounding plains.

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大多数最大的火山都与塔尔西斯凸起有关，但在北部平原上发现了许多较小的火山。

Most of the largest volcanoes are associated with the Tharsis bulge, but many smaller ones are found in the northern plains.

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