# Event changes or expiration

When an alert changes, issue a new alert that refers to the previous alert.
Don't change or remove the existing alert from your feed. After an appropriate
amount of time like 24-48 hours, remove canceled, updated, or expired alerts
from your feed.

Handle event changes or expiration in the following way:

- An `UPDATE` or `CANCEL` `<msgType>` must include at least one `<references>` element.
- There are three ways to cancel events, in order of preference:
  1. Set an `<expires>` `dateTime` value for each event. In the message description, set the expectation for this alert to end on its own.
  2. Issue a new `<alert>` message that contains `<msgType>` `UPDATE`, `<responseType>` `"All Clear"`, and `<expires>` a short time in the future.
  3. Issue a new `<alert>` message with `<msgType>` `CANCEL`. In the `<references>` element, refer to the original alert to cancel.

## Examples

    <alert xmlns="urn:oasis:names:tc:emergency:cap:1.2">
      <identifier>PAAQ-4-mg5a94</identifier>
      <sender>wcatwc@noaa.gov</sender>
      <sent>2013-01-05T10:58:23-00:00</sent>
      <status>Actual</status>
      <msgType>Update</msgType>
      <source>WCATWC</source>
      <scope>Public</scope>
      <code>IPAWSv1.0</code>
      <references>wcatwc@noaa.gov,PAAQ-1-mg5a94,2013-01-05T09:01:16-00:00
       wcatwc@noaa.gov,PAAQ-2-mg5a94,2013-01-05T09:30:16-00:00 wcatwc@noaa.gov,
       PAAQ-3-mg5a94,2013-01-05T10:17:31-00:00</references>
      <incidents>mg5a94</incidents>
      <info>
        <category>Geo</category>
        <event>Tsunami Cancellation</event>
        <responseType>None</responseType>
        <urgency>Past</urgency>
        <severity>Unknown</severity>
        <certainty>Unlikely</certainty>
        <onset>2013-01-05T10:58:23-00:00</onset>
        <expires>2013-01-05T10:58:23-00:00</expires>
        <senderName>NWS West Coast/Alaska Tsunami Warning Center Palmer
         AK</senderName>
        <headline>The tsunami Warning is canceled for the coastal areas of
         British Columbia and Alaska from the north tip of Vancouver Island,
         British Columbia to Cape Fairweather, Alaska (80 miles SE of
         Yakutat).</headline>
        <description>The tsunami Warning is canceled for the coastal areas of
         British Columbia and Alaska from the north tip of Vancouver Island,
         British Columbia to Cape Fairweather, Alaska (80 miles SE of Yakutat).
         - Event details: Preliminary magnitude 7.5 (Mw) earthquake / Lat:
         55.300, Lon: -134.900 at 2013-01-05T08:58:20Z Tsunami cancellations
         indicate the end of the damaging tsunami threat. A cancellation is
         issued after an evaluation of sea level data confirms that a
         destructive tsunami will not impact the alerted region, or after
         tsunami levels have subsided to non-damaging levels.</description>
        <instruction>Recommended Actions: Don't re-occupy hazard zones until
         local emergency officials indicate it is safe to do so. This will be
         the last West Coast/Alaska Tsunami Warning Center message issued for
         this event. Refer to the internet site ntwc.arh.noaa.gov for more
         information. </instruction>
        <web>http://ntwc.arh.noaa.gov/events/PAAQ/2013/01/05/mg5a94/4/WEAK51/WEAK51.txt</web>
        <parameter>
          <valueName>EventLocationName</valueName>
          <value>95 miles NW of Dixon Entrance, Alaska</value>
        </parameter>
        <parameter>
          <valueName>EventPreliminaryMagnitude</valueName>
          <value>7.5</value>
        </parameter>
        <parameter>
          <valueName>EventPreliminaryMagnitudeType</valueName>
          <value>Mw</value>
        </parameter>
        <parameter>
          <valueName>EventOriginTime</valueName>
          <value>2013-01-05T08:58:20-00:00</value>
        </parameter>
        <parameter>
          <valueName>EventDepth</valueName>
          <value>5 kilometers</value>
        </parameter>
        <parameter>
          <valueName>EventLatLon</valueName>
          <value>55.300,-134.900 0.000</value>
        </parameter>
        <parameter>
          <valueName>VTEC</valueName>
          <value>/O.CAN.PAAQ.TS.W.0001.000000T0000Z-000000T0000Z/</value>
        </parameter>
        <parameter>
          <valueName>NWSUGC</valueName>
          <value>BCZ220-210-922-912-921-911-110-AKZ026&gt;029-023-024-019&gt;
          022-025-051258-</value>
        </parameter>
        <parameter>
          <valueName>ProductDefinition</valueName>
          <value>Tsunami cancellations indicate the end of the damaging tsunami
           threat. A cancellation is issued after an evaluation of sea level
           data confirms that a destructive tsunami won't impact the alerted
           region, or after tsunami levels have subsided to non-damaging
           levels.</value>
        </parameter>
        <parameter>
          <valueName>WEAK51</valueName>
          <value>Public Tsunami Warnings, Watches, and Advisories for AK, BC,
           and US West Coast</value>
        </parameter>
        <parameter>
          <valueName>EAS-ORG</valueName>
          <value>WXR</value>
        </parameter>
        <resource>
          <resourceDesc>Event Data as a JSON document</resourceDesc>
          <mimeType>application/json</mimeType>
          <uri>http://ntwc.arh.noaa.gov/events/PAAQ/2013/01/05/mg5a94/4/WEAK51/PAAQ.json</uri>
        </resource>
        <area>
          <areaDesc>95 miles NW of Dixon Entrance, Alaska</areaDesc>
          <circle>55.3,-134.9 0.0</circle>
        </area>
      </info>
    <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
      ...
    </Signature>
    </alert>