Answer:
6.4 m/s
Explanation:
Given that :
The average width of the Colorado river = 100 m
Average depth of the river is = 8 m
Therefore, area = 
Speed of the river, 
After the lava falls on the river,
Width of the river becomes = 25 m
Depth of the river became = 15 m
Therefore, area = 
Now, since the volume flow rate of the Colorado river is same, then from the Continuity equation,


∴ 

= 6.4 m/s
Therefore, the speed of the river in this location is 6.4 m/s