If you have selected hours to be approved by your organizer upon submission, this notification will be triggered after each time submission.
To enable or disable Hour Approval Notifications go to Organizer Dashboard
In the Settings menu, go to Volunteers tab and you will see the question Do you want to approve each hour submission? Select Yes or No.
You can enable to disable this notification at any time. The notification will by default go to the organization's approver. If there is no approver, then the notification will be sent to the coordinator, manager, or owner (in that order depending on the organization).
For more help on approving hours, read this!