You can delete triggered alerts.
Procedure
From the navigation pane, go to Monitoring > Alerts.
The Triggered alerts page appears.
To delete alerts, do one of the following:
To delete individual alerts, select the check box for the alert, and then click Delete.
To delete all of the alerts, select the check box in the table header and click Delete.
Note: If there are pinned alerts in the list, they are deleted.