Assuming that you're talking about an iCloud calendar, those alerts are being placed there because of a setting you have on your iPhone, iPad or Mac. It's a default that places alarms on all new events.
On your iPhone or iPad
Go to Settings
Tap on Mail, Contacts, Calendars
Under Calendars tap on Default Alert Times
Make sure Events and All-Day Events are set to None
On your Mac
Under Calendar click on Preferences
Do the following for all Selectable Accounts
Make sure Events and All Day Events are set to None
You can also manually open each trip in iCal and turn off the notification.