Questions: What was the cause of flooding in the 1993 upper Mississippi River flood? Heavy snowmelt in Canada sent large volumes of water down the river in the spring. A dam failed because it had been built in a risky place near a fault. Persistent thunderstorms caused large amounts of rainfall over a several-state region. Winter produced rain that melted snow that was on the ground.

The answer is the third one: Persistent thunderstorms caused large amounts of rainfall over a several-state region.

Explanation for each option:

1. Heavy snowmelt in Canada sent large volumes of water down the river in the spring: This option is incorrect because the primary cause of the 1993 upper Mississippi River flood was not attributed to snowmelt from Canada. While snowmelt can contribute to river flooding, it was not the main factor in this event.

2. A dam failed because it had been built in a risky place near a fault: This option is incorrect. The 1993 flood was not caused by a dam failure. The flooding was primarily due to natural weather conditions rather than structural failures.

3. Persistent thunderstorms caused large amounts of rainfall over a several-state region: This option is correct. The 1993 upper Mississippi River flood was primarily caused by persistent and heavy rainfall from thunderstorms over a wide area, which led to the river and its tributaries overflowing.

4. Winter produced rain that melted snow that was on the ground: This option is incorrect. While rain on snow can contribute to flooding, the 1993 flood was mainly due to the excessive rainfall from thunderstorms rather than rain-induced snowmelt.

In summary, the 1993 upper Mississippi River flood was primarily caused by persistent thunderstorms that resulted in significant rainfall over a large region.